On Windows, just use the built-in Windows Defender. On Linux, I recommend ClamAV + ClamTK. On Android, Hypatia.

If you think you have malware, this is a pretty good guide to remove it.

I'd also strongly recommend using and configuring a content blocker like uBlock Origin in your browser, as well as using a DNS level blocker like NextDNS.

If you have a multilayered setup like this, then I think you're pretty good and it'll be not impossible, but much harder to get malware or be infected. Just use common sense as always.