The overarching book recommendations answer has been quite helpful for a lot of people me included. Is there / should we make a similar one for online lectures? Or maybe add it to this answer. I mean there are gems in youtube like Frederic Schuller's Lectures on GR and QM whose contents are not picked up from any book easily and whose formatting is quite unique. Feel like a storehouse for such gems would be greatly helpful for many of us.
The more or less consistent practice about resource-recommendations questions so far is that they in principle don't distinguish$^1$ between books, websites, online lectures, whether they are free or not, etc. This is to avoid a proliferation of closely related resource-recommendations questions. [There is already a division into different levels of a topic: beginners, advanced, etc. There are currently (November 2021) more than 2000 resource-recommendations questions.]
For this reason, Phys.SE usually doesn't allow resource-recommendations questions that only asks for e.g. online lectures but not books. This alone means that OP's proposal is a non-starter.
Other objections are that online content is prone to link-rot, and that it would require curating from dedicated users. It is symptomatic that the main resource recommendation question was closed in 2013. See also Good list, bad list and various other meta discussions on resource-recommendations.
$^1$In contrast, the answerers are welcome to focus on whatever type of resources they prefer (as long as they comply with the Phys.SE policy.)
There is a problem with this idea: links becoming dead over time.
Books are books and they can become difficult to find over time, but the reference to the book does not become out of date. The reference is always valid (e.g. an ISBN).
However, online lectures can disappear dues to the many forms of link rot. Some sources are better than other for this, but none of them are really permanent references. YouTube videos can be removed or blocked and written texts can be removed or the host site reorganized or the material removed when people e.g. change job.
As we generally prohibit (at or least strongly discourage) answers that rely on links, this seems to imply that a category of question which will result in answers completely relying on links is not really within the current way we do things.
I'm not sure we can find a way to fit this type of question within the rules. It's not like we don't already post such links, but if a post has answers with nothing but these types of links, that seems problematic in the long run.
I'm not exactly opposed to the idea, but we need to understand that we're opening the site to the possibility of dead answers moving forward. Is that really useful to members?