This question might be weird, I wouldn't feel bad if it is closed.
I know that MathOverflow is for mathematicians and math StackExchange for people studying math at any level. But questions like "How is this theorem of mine?" or "Please review this article" will get closed immediately. I don't think so, but is there a StackExchange site that answers these types of questions? If not a StackExchange site, is there any trusted site for this purpose?

3$\begingroup$ That's what colleagues & journals are for. $\endgroup$– Gerry MyersonOct 28 '20 at 12:09

1$\begingroup$ Somewhat related older post on this meta: Community PeerReview in Mathoverflow. You can find also some related discussions: Submitting a paper for review, Are requests for proof reading written articles appropriate on MSE?, etc. $\endgroup$– Martin SleziakOct 28 '20 at 14:21

1$\begingroup$ Also these questions on [mathoveflow.se] might be of interest for you: Are there any good websites for hosting discussions of mathematical papers? and Math Annotate Platform? There is also this question on Mathematics: Where to get peerreviewed before submitting a paper to journal? (And maybe you can find some other posts on this  this is what I was able to find.) $\endgroup$– Martin SleziakOct 28 '20 at 14:24
It sounds like a natural demand. I'm not aware of its existence at the moment. Journals (not colleagues) have this role of reviewing, but the idea (public posting and reviewing) would be an interesting alternative.
There is a practical difficulty. From my observation so far, the majority the posts appearing and which are (explicitly or in disguise) reviewing requests, are asking if some bunch of computation can be a useful approach, or even a proof, to the Riemann hypothesis, Collatz conjecture, factorization of large integers, etc. In remaining cases, these are often long disorganized sequences of ideas and computations, more or less hard to decipher.
Hence, a site which would do this without strict moderation would be overwhelmed with lowquality requests (and hence not very attractive to the research community). Designing such a site with adequate moderation is an interesting idea and we can hope it will exist at some point.

$\begingroup$ Seems like a good idea for area 51. $\endgroup$– user167505Oct 28 '20 at 14:45

4$\begingroup$ @epic_math I am not really sure about that. You can see that there suggestions for new sites lead nowhere: Area 51 Mathematics Open Community Reviews and area 51 proposal  Math review. (They are not exactly the same as your suggestion, but they definitely share some common features.) $\endgroup$ Oct 28 '20 at 16:15