Hi Phil,
Great question! We have instructions on configuring the user-agent header in the documentation here.
Please note that Linux Mint isn't an officially supported distribution, but as you said, it is a focal-based Ubuntu distribution, so it should work just fine. However, we'd like to hear about any ABI complications if you do run into them.
I hope you're enjoying RStudio Package Manager and these binaries speed up your workflow 
Cheers,
Tyler