10+ years freelancer. I have virtual machines for each client, and a personal one where i test my stuff. Currently ~10 machines sitting on my PC hard, plus 20+ backed up on a separate backup hdd specially made for this. And all are backed also in the cloud, on encrypted volumes, under different providers with thousands of accounts each, all managed by a password manager (I made my own pwd manager for my own needs).

This setup allows me full separation for each client plus my own stuff. Personally I think this is the best solution. Only downside is that requires a good internet connection, which in my country is a non-issue