Is it true that the Maalikis allow plucking the eyebrows for women other than those who are forbidden to do anything to beautify themselves?

Yes, what you have read is one of the official views of the Maalikis. It says in al-Fawaakih ad-Dawaani, which is a book about Maaliki fiqh (2/509):

Plucking refers to pulling out the eyebrow hairs so that the brow becomes thin and beautiful.

Moreover, it was narrated from ‘Aa’ishah (may Allah be pleased with her) that it is permissible to remove hair from the eyebrow and face, and this supports the view mentioned above, according to which it is permissible for a woman to shave all of her hair except that on her head.

Based on that, the hadith is to be understood as referring to the woman who is forbidden to use any adornment, such as one whose husband has recently died and one whose husband is missing. End quote.

However, the report of ‘Aa’ishah (may Allah be pleased with her) which they quoted as evidence for it being permissible was quoted by al-Haafiz ibn Hajar (may Allah have mercy on him), and he said:

At-Tabari narrated via Abu Ishaaq, from his wife, that she went to see ‘Aa’ishah when she was a young woman who liked to beautify herself, and she said: Can a woman remove hair from her forehead [to beautify herself] for her husband? ‘Aa’ishah said: Remove that which is bothersome as much as you can. End quote from Fath al-Baari (10/378).

This was also narrated by Ibn al-Ja‘d in al-Musnad (451) with the same isnaad. It was classed as da‘eef (weak) by Shaykh al-Albaani (may Allah have mercy on him) in his book Ghaayat al-Maraam (no. 96) because the wife of Abu Ishaaq, who narrated it from ‘Aa’ishah, is unknown; her name was al-‘Aaliyah.

Ad-Daaraqutni, in as-Sunan (3/477), also deemed her to be unknown and stated that her report cannot be quoted as evidence. Something similar was suggested by ash-Shaafa‘i in his book al-Umm (4/74).

If it is proven that the report from ‘Aa’ishah (may Allah be pleased with her) is da‘eef, then it cannot be quoted as evidence.

Even if we assume that it is saheeh (sound), it may be that ‘Aa’ishah (may Allah be pleased with her) did not hear the hadith that forbids plucking the eyebrows, and she issued this fatwa on the basis of her own understanding.

It was narrated that ‘Abdullah ibn Mas‘ood (may Allah be pleased with him) said: May Allah curse the one who does tattoos and the one who has a tattoo done, the one who has her facial hair plucked, and those who file teeth for the purpose of beautification, changing the creation of Allah. Why should I not curse those whom the Messenger of Allah (blessings and peace of Allah be upon him) cursed, when it is in the Book of Allah? “And whatever the Messenger has given you – take; and what he has forbidden you – refrain from” [al-Hashr 59:7]. Narrated by al-Bukhaari (5931) and Muslim (2125).

The word “the one who has her facial hair plucked” is general in meaning, and the basic principle regarding what is general in meaning is that it is general in application, and it should not be taken as being limited to a particular situation except on the basis of evidence.

Muhammad al-Ameen ash-Shinqeeti (may Allah have mercy on him) said:

The correct view and the view of the majority is that we should believe that it is general in application, without trying to look for a reason to make it specific to certain situations, because the wording of the hadith is general and should be taken as being general in application. If we find some evidence to indicate that it is limited to a specific situation, then we may act accordingly.

We have noted above that what appears to be the case is that we should understand the hadith as being general in meaning and apply it as such, unless there is evidence to indicate otherwise.

Undoubtedly the hadith is general in application and should be applied to all individuals, as is quite clear. End quote from Mudhakkirah Usool al-Fiqh (p. 261).

And he (may Allah have mercy on him) said:

It is well established in usool al-fiqh that you cannot understand a hadith that speaks in general terms as applying only to specific people unless there is a report that we must refer to (and cannot ignore). End quote from Adwa’ al-Bayaan (5/83).

With regard to the words of ‘Aa’ishah (may Allah be pleased with her) – even if we assume that the report is saheeh – ‘Abdullah ibn Mas‘ood (may Allah be pleased with him) disagreed with her. If the Sahaabah disagree on an issue, the view of one of them is not regarded as evidence to refute the other view; rather reference should be made to what may be understood from the religious texts.

Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:

With regard to the views of the Sahaabah, if they became well-known and no one objected to them during their time, then their views are regarded as proof and evidence according to the majority of scholars, but if they differed, then their dispute is to be referred to Allah and His Messenger.

The view of one of them cannot be taken as ultimate proof when others had different views, according to scholarly consensus.

End quote from Majmoo‘ al-Fataawa (20/14).

Al-Bukhaari (4886) and Muslim (2125) narrated from ‘Alqamah, that ‘Abdullah said:  May Allah curse the one who does tattoos and the one who has a tattoo done, the one who has her facial hair plucked, and those who file teeth for the purpose of beautification, changing the creation of Allah.

When Ibn Mas‘ood (may Allah be pleased with him) narrated this hadith, a woman from the tribe of Banu Asad who was called Umm Ya‘qoob said to him: I think your wife does that. He said: Go and look. So she went and looked, and she did not see anything of what she had claimed. He said: If she was like that, I would not have stayed with her – meaning that he would have divorced her and would not have lived in the same house as her.

The conclusion of this story is that his wife had no reason not to adorn herself for him. It was narrated that the discussion between this woman and Ibn Mas‘ood had to do with plucking the eyebrows in particular. Ash-Shaashi narrated in al-Musnad (2/256), with his isnaad from Qabeesah ibn Jaabir that he said: I went with an old woman of Banu Asad to see Ibn Mas‘ood in his house. He noticed that her forehead was very clear, so he said: Do you shave it? She got angry, then she said: The one who shaves her forehead is your wife! He said: Go in and see her. If she does that, then I will have nothing to do with her. So the old woman went, then came back and said: By Allah, I do not think she does that. Ibn Mas‘ood said: I heard the Messenger of Allah (blessings and peace of Allah be upon him) curse women who have their facial hair plucked, those who file the teeth and those who have tattoos done, who changed the creation of Allah, may He be exalted. This hadith was classed as hasan by al-Albaani in Aadaab az-Zafaaf (p. 203-204).

Conclusion: the view of the Maalikis regarding this issue is not the more correct view, because it is limiting the application of the hadith mentioned without any evidence to support doing so.

And Allah knows best.