It seems as if all companies want to embrace, engulf and extinguish. Gmail is still highly usable for me, using mutt, but, for example, my latest pet peeve is slack. When they started, you could use irssi or weechat with almost no work. Then they changed it in 2016, irssi became a bit of a pain, you had to use bitlbee and, as I remember, it was always a bit of work--such as you had to get a legacy token each time. Fortunately, there is a weechat_slack.py plugin and weechat is still easy. But as of tomorrow, i think, they're removing legacy tokens. (I think you can still use old ones that you've set up with weechat, I guess I'll find out this week)
Anyway, aside from "old guy ranting" the point here is that it seems so many companies start off saying how they're just here to work with you, and as they get more popular, make it so that one has to use their bloated GUI app.
But, back on topic, right now at least, gmail, using getmail to fetch mail and msmtp to send it, works without issue for me with neomutt on either FreeBSD-12.1 or CentOS-8.