Thunderbird I use each day on my Linux desktop. It’s ok, better than the others I tried.

I have different email addresses I manage.

There are probably dozens of ways to create a non Gmail email, depending on your tech level with domains.

If you want a custom domain, just purchase one at any domain seller. Example liner.me , limer.name etc, there are dozens of things you can choose from and will cost very little to a lot depending on your choice.

Then once you have that , most of the major domain providers offer email service without getting complicated. Or, you can go next level and take your new domain to one of many email companies where they hook you up. Or, you can do this yourself.