I'm running Windows 10 Pro (20H2) and recently discovered it had stopped going to sleep automatically. The Sleep function worked OK manually and waking up was not an issue, but my Sleep settings were simply not working. I followed the numerous postings on this issue and tried a number of 'solutions', but none of them worked!
However, I subsequently discovered that it was a Microsoft Edge setting that was causing the problem (see image below).
I disabled the 'Start-up Boost' and 'Continue running...' options and my problem was instantly resolved. I haven't tried turning the 'Continue...' option back on to see what effect it has, but I'm just pleased Sleep is working automatically again. Hope this helps?
Sweet dreams!