Gmail has three main features that matter (to me at least) -- and they are huge, very important features. And as much as I don't like this fact, using their official web or mobile clients are the only way to get them:

1. Accurate, deterministic, fast search of your email

2. Whatever they call the categorized inbox, I use "Primary," "Promotions," and "Updates."

3. Labels implemented as labels, not mapped clumsily onto the "Folder" concept.

If I were told I had to not use the Gmail UI, I would 100% switch to another email provider immediately, as using Gmail the service with a vanilla IMAP client is way worse than just using a normal email host with the same.

Thunderbird works well for my needs. I just want to see my emails categorized in reverse chronological order. I don't expect or want any kind of filtering; I would just Sieve filters for that (running on my own server). Perhaps I am just old fashioned. Should I want AI assistance to write an email, I would fire up a local model such as GPT-OSS. Local models are more than capable for trivial tasks like this, and a smaller model on CPU only would also work.