If your PC is compromised it's pretty much game over, using a password manager does not really worsen the damage in that scenario At that level of compromise they can probably add a root cert, MITM your connections, and grab your passwords anyway.

If you're concerned, you could use separate files for different levels of security, which would give you the theoretical ability to compartmentalize the loss. But again, if you're compromised to that extent it's game over, there is nothing you can do that will allow you to operate securely on untrusted hardware/OS, you simply can't let that happen.

It's not like that's an unreasonable goal, the combination of Ublock Origin, Windows Defender, and common sense have kept my systems clean for 10 years now.