Two non-free nor self hostable options from personal recommendation:

1. Fastmail is the best I've seen. Australian / 5 eyes, so not ultra private but they're open about what access they give on court order. Web ui is super fast. Good compatibility. Good privacy.

2. I was on Protonmail before FM. Everything is good, except speed. Each mail takes 5s or so to open due to it being E2EE and Encrypted at rest. Can't beat it for privacy (Swiss, so as good as that gets), but needs special tools to use with a normal browser or as a gateway (It's own bridge tool that acts as a decrypting proxy). Those tools are good, but they're an extra layer of bloat and delay.

You need to understand that nothing good will be free unless it's selling your information. If you insist on free, then Gmail is good from a usability, but they're reading your email and using that content against you. I accepted that for years, but feel the balance is too much against me now.

Self-hosting email: Personal email is the one and only service I don't selfhost, and that's despite me being a sysadmin and with some 35 years experience of doing it (Before the internet was widely available, I was a mail provider on BBSs using UUCP and Fidonet, then ran on-prem email using various technologies for SMEs) so I've got a few miles and to answer your questions, some opinions about mail.

Email is something I know how to do, but as the years have gone on, selfhosting it has got harder and less reliable. I used to spend hours tuning mail filters to beat spam, and emails going out would end up in others' spam or just be silently dropped. Exchange and Gmail in particular would silently drop email they didn't trust. You just wouldn't know your message didn't arrive. Email, after all, is over seven decades of people abusing it, others trying to stop that abuse, new abuse methods - it's an arms race that now, more than ever due to AI, is accelerating. Whilst selfhosting an email system is very easy, making it reliable enough when you don't control most of the pieces, is a fulltime job and even then, you will always lose some outbound mail if your IP isn't commercially zoned. It's not a conspiracy by Big Mail, it's that so many residential IPs have been compromised and send spam.

Somewhere along the line, I figured I'd let someone else worry about it. That was Gmail for a long time but I'm taking privacy more seriously these days so I now pay someone to do my email. They will always be better able to do it than I am due to scale and visibility and it being their fulltime job.

If you want to learn about email, there's few better ways than selfhosting it and if that's the objective, then using low-level tools rather than a pretty all-in-one package will teach you more. But if you just want reliable email, then Gmail and accept they are selling information about you, or pay a reputable third party.