But i think yes since i'm not the lawmaker.
Everyone should be free to advertise or promote any of his/her things provided the link is not malicious.
Sometimes we do give credit by sharing links to an external source project, i don't think there's a difference between that and sharing my own youtube/instagram/twitter link in any of my code
Yes, Mirielle's answer is perfect.
Adding on, if any of the links share information that can dangerously identify you e.g. a personal Facebook (it can expose your residential location, family, daily routine, everything about you, etc.) then moderators may step in, especially if the person is underage.
And if you spam it outside just your code and feed then its not permitted.
Its more relaxed now ever since the introduction of the feed feature, but spamming outside, "monetary gain" links, and malicious links are when action has to be taken.
Face reveals, country, school, workplace I guess is permitted since SL has a place to put it.
There are many reasons that external links are not permitted but YouTube seems to be one of those acceptable as it does not directly / potentially to personal information however if found to lead to viruses or malware or a risky or other deemed bad site(s) then the code or post may be blocked / deleted / or whatever necessary steps to insure the safety of the app and community-at-large ... this may be done by the moderator(s) and or by SoloLearn Staff.
thanks 「ＨＡＰＰＹ ＴＯ ＨＥＬＰ」
Except if there's a rule that says "DO NOT SHARE A LINK"
edit: talking about an approved rules made by the actual sololearn( that can be accessed from their site's details page,) not the one made by moderators
And since there's not, i'll feel free to share anything i want provided it's not against some other rule(s)