Okay so, after exchanging quite some messages with nop-templates team, i would like to add some stuff that i didn't find relevant in initial post. First thing, we are testing 4.1 version but our 3.9 works without any issue at all. Next, which i didn't know its considered that big, database that we have is 18000 products with 120000 specifications, 40000 pictures... We are using this DB since 2.9 (i think) and since then it grew from 6k to todays 18k of products. Not a single time we had any issues with nop, not performance not any other way. It's not heavily customized, but only some minor tweaks which do not affect performance at all (checked).
A lot of people pointed me to this topic: https://www.nopcommerce.com/boards/t/54986/nopcommerce-410-high-memory-usage-and-how-weve-handled-it.aspx but i just fail to see how can memory problem (which I don't have) can affect cpu over usage. I checked that post and file is just as that in nop, they already applied fix to newest build. Also, i got reply that some other process might affect cpu, that is also not an issue, because you can clearly see when you log in to server that .NET Core Host consumes all power that is left on cpu whenever page on site is loaded. Using mini profiler i found out that it takes entire 2 minutes to load one page of category, when 2 users in same time try to load it, time goes up to even 3 minutes. When i am lucky, page loads for 30-60 seconds.
I tried everything, disabling plugins, using default theme, reinstalling and reupgrading... nothing works. Every plugin that has AJAX works just as bad as site, and as you can guess everything combined makes site completely useless. If there is any way that Andrei will read this post and try to help with fixing it, i would be more than grateful.