Maximun Capacities of Ubuntu Server 20.04
Solution 1:
Given the way the question is asked, I am curious to know how much research you have done prior to visiting this site. A lot of the information you seek can be found on Ubuntu.com.
That said …
Supported architectures
⇢ x64 / ARM / Power / s390x / others (if you’re willing to do the work)
Supported CPU cores
⇢ All of them. There is no CPU in existence with more cores than a modern Linux kernel can handle.
Maximum supported RAM
⇢ 16EB (though many enterprise motherboards top out at 2TB per CPU socket)
Solution 2:
here are some references which relate to your multi-faceted question:
Ram
Architectures
Cores