1st the idea is that makes a handshake between you computer and the client so you can see what they get and hopfully fix it... "provide remote support for free" is misleading imo
now the need to sign in = yes but what you sign in as is the correct question Microsoft account = email... there is no law saying you can only use 1 email and if you have more than 1 then linking them together is optional
Only the user offering the remote assistance needs to sign in for Quick Assist to function. There is no way around that. The reason for the sign-in is that you are signing into Microsoft's RDP relay service.
If you want a free option for remote assistance with minimal fuss I would look into 'reverse vnc'. You will need to create the package and when someone needs assistance they will need to have that package or you can host it on some site for them to download.