Thunderbird (meh) vs. alternative(s) that will work for Gmail's demand for OAUTH2

Please pardon my very plain tastes !?!
I used to adore Thunderbird around version 2 or 3, but since then its become too cluttered & 'modernized' for my liking.

The setup of SeaMonkey's email client suits me well - but as a whole it is less than stellar to install, use - and likely also fails the OAUTH2 deal as well.

My query:
Are there any really great alternatives that DO support OAUTH2 whilst still being quite plain ??

Thanks for any helpful pointers !!

Claws Mail would be far more to my liking it seems - but sadly with gmail's latest changes enforcing OAUTH2 very soon, that will likely cease working.

OK, replying to my own query as I have forged ahead in my own manner & come to some conclusions...

To start with, Claws Mail is basically unsupported (yes they have a list - I'll pass on that, thanks) - so I will also totally pass on messing with that option after all.

Finally found a real, working way to get Seamonkey to install, which is very cool IMO - after trying & giving up before because all the info I found at that time pointed to...nothing working.
Simple answer is - they moved it - how silly is that ?!?
Got a DEB of its latest version, made a small adjustment to accomodate it, and presto - installed now.

Tested it via a Gmail account that is seldom used - gave it the needed OAUTH2 permission, and watched it sit there for 1/2 hour without ever logging in.
Then tried it a 2nd time - same result - so I call that a solid failure.

Gave in & tried the same with Thunderbird (meh) and it sailed right into the account & worked immediately - so I guess I'll just have to use Gmail via that & just try to find my old favourite theme for it, if that still exists.

The good news for me is that I'll just use Seamonkey for my non-OAUTH2 email & that will suit me fine as most of what I get comes in that way.