Praise be to Allah.
It is proven that the Prophet (blessings and peace of Allah be upon him) forbade men to imitate women and women to imitate men.
It was narrated that Ibn ‘Abbaas (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace of Allah be upon him) cursed men who imitate women and women who imitate men.” Narrated by al-Bukhaari, 5885.
It was narrated that Abu Hurayrah (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace of Allah be upon him) cursed men who wear women’s clothing and women who wear men’s clothing.
Narrated by Abu Dawood, 4098; classed as saheeh by Shaykh al-Albaani (may Allah have mercy on him).
It says in al-Mawsoo‘ah al-Fiqhiyyah, 11/268: There is no difference of opinion among the fuqaha’ that it is haraam for men to imitate women in their movements, soft speech, adornments, clothing and other things that are exclusively theirs according to custom or nature… Ibn Daqeeq al-‘Eid gave as a guideline on what it is haraam to imitate them in as being whatever is exclusively theirs, whether it is the thing itself or the way it is made or the fact that it is more commonly made for women, and the converse is also true. End quote.
See also the answer to question no. 81994
It does not mean that something is not the kind of imitation that is haraam if there are people who wear the item concerning which there is the fear of it being imitation in a certain country or at a certain time. It is very rare to find none of it at all. Rather what may take it out of the category of being haraam is if it becomes widespread in that particular place, and it becomes commonly practised and like a custom, without anyone objecting to it, to the point that the one who does it is no longer regarded as odd, and people of dignity and decency would not refrain from it.
Al-Haafiz Ibn Hajar (may Allah have mercy on him) said: at-Tabari said: What is meant is that it is not permissible for men to imitate women with regard to the garments and adornments that are only for women, or vice versa.
I say: This applies to ways of speaking and walking. As for styles of clothing, that may vary according to the differences in customs from one land to another. There may be some people who do not differentiate between the clothing of their women and their men, but the women are distinguished by observance of hijab and covering.
End quote from Fath al-Baari, 10/332
In the commentary on al-Qawaa’id al-Fiqhiyyah by Shaykh Sa‘d ibn Naasir ash-Shatri it says: Custom (al-‘urf) in any country must meet certain conditions in order for it to be acceptable in sharee‘ah. The conditions for custom are four:
The first condition is that the custom should be consistent and widely practised; it should not be inconsistent because if it is inconsistent and not widely practised, it is not called custom. This is what they expressed by saying: What counts is what is widely known and practised, not that which is rarely practised. End quote.
In al-Mawsoo‘ah al-Fiqhiyyah (30/58) it says: What is important with regard to custom is that it should be consistent or widely practised. What is meant by consistent is that the custom is ongoing and persists so that it does not disappear in different situations. What is meant by widely practised is that it is done a great deal, and is not done. That is because consistency and being widely practised proves that the custom is definitively well established and well known. As-Suyooti said: It is regarded as a custom if it is consistent; if it is not consistent then it is not regarded as a custom. End quote.
With regard to the necklaces that you asked about, it is not known in your country (Saudi) that this custom is consistent, and it is not widely practised among men without any objection; rather hardly anyone does it except effeminate men and their ilk, or those who imitate women or evildoers. So it is not permissible for you to wear it for that reason.
See also the answer to question no. 148059
And Allah knows best.