You don't need a third party blog, it's in the documentation[1]: "All versions of the AMD Athlon 64 processors and their clones are supported."
The other drivers are the ones you need to worry about -- check the man pages, which list the supported hardware. For example: https://man.openbsd.org/radeon.4
The attitude isn't "You shouldn't need documentation". The attitude is "OpenBSD should ship with documentation good enough that nobody feels the need to write up the results of sleuthing around".
Ryzen works great, and will likely improve over time. The Vega GPU that accompanies some models is unsupported, however, if you can get a slightly older AMD card things will be better on the graphics side, but this is only important if you care about some light gaming or desktop frills.
The other drivers are the ones you need to worry about -- check the man pages, which list the supported hardware. For example: https://man.openbsd.org/radeon.4
The attitude isn't "You shouldn't need documentation". The attitude is "OpenBSD should ship with documentation good enough that nobody feels the need to write up the results of sleuthing around".
[1]https://www.openbsd.org/amd64.html