I remove defender on my installs as it’s resource heavy and it doesn’t provide me any additional security that I require. I don’t download any software to the PC aside from the run-of-the-mill apps, so I don’t need Defender constantly scanning my system and files.

I don’t replace the anti-virus with anything. You can use the Windows Malicious Software Removal Tool (MSRT) to scan files if needed but I haven’t needed it yet. For a firewall I use Simplewall, which is a fantastic lightweight FOSS app I recommend to everyone