I've never in my life seen an ad in Gmail mobile app in-line as though it were something in your inbox. I get really frustrated at the indignance over "ad company does ads and you're mad" as if there's not a difference when things get escalated.
They've been picking up the density, for sure. I think adblock has also frequently worked on the webUI if you've used firefox, i'm not sure if they've updated it to get around ublock.
FAANG and the other high-cap tech companies have been cashing in on their market dominance these last few quarters - they're all getting bad. That's not a good sign if you're an average joe; it means you'll be bombarded with tracking and ads (even more than now) AND I think it's a bad sign for market stability. People have been predicting another recession for a while, but that signal is getting louder I think.
They started putting ads in the mobile app a while ago. I think I first noticed a couple years ago? I had been using Inbox until that got shut down, then used the web UI for the most part. I've tried a few other app options, but the only one I like is $10/mo just for the UI. Not even a full email address, just a UI for Gmail.
I don't recall seeing ads in the phone app, however, just the webapp, so perhaps that is new? Which makes some kind of dark sense given less people use computers to do things anymore, and every tech company is trying to pull off increasingly maximum grift over the last few years.