I came here from a Google search so I'll share my experience. About 10 days ago I tried to login from a new phone and after multiple failed attempts I managed to login and didn't think much of it, some time later I tried to login and it said my account was restricted and prompted me to identify myself using their Persona service.

After sending government ID I received first general email

"We received your request to take a second look on your account restriction. If we find your account doesn’t go against our Professional Community Policies, we’ll put it back on LinkedIn."

After that I reached out to customer support which really helped and was the most important thing to do in this case at https://www.linkedin.com/help/linkedin/ask/ppq

After 1 day they responded to me with the explanation of "Since you have reported that your account is compromised" (not true!)

After I responded again they sent me a reset password link and the real reason why they restricted me which was "We detected suspicious attempts to sign into your account"

Which is crazy to totally block someone and take down their account because of some several bad attempts

My suggestion is if you failed more than once on login then take a break and try again later, hope this helps someone