My general feeling is that if someone wants to install a hardware rootkit on my extremely boring home servers, it’s highly unlikely that I’ll be able to stop them. I can do best practices (like not exposing things publicly), but ultimately I can’t stop Mossad; on the other hand, I am an unlikely target for anything other than script kiddies and crypto miners.
Sure, but if you already know since before that this specific cryptominer has been found together with rootkits, and you know rootkits aren't as easy to detect, what's your approach to validate if you're infected or not?
Maybe I'm lucky that I can tear down/up my infrastructure relatively easily (thanks NixOS), but I wouldn't take my chances when it's so close to private data.
That's my point – you can do best practices all day long, but short of observing sudden shifts (or long-term trends) in collected metrics, you're not going to be able to notice, let alone defend, against sophisticated attacks. There has been malware that embeds itself into HDD firmware. Good luck.