MacBook Pro running hotter than it used to, and I can't figure out what changed

I had a 2014 MBPr 15" for about 5 years, and bought iStat Menus on about the first day. I've always kept an eye on the CPU temp. That laptop usually ran in the high-90's (degF) during normal, web-browsing use.

I upgraded to a 2019 MBP 15" a few months ago, and worried about the thermal issues. This machine has usually run just a little over 100 degF. Like, 102-104. I've been extremely satisfied that Apple had solved the "thermal issues" with the first version of the TouchBar MBP's in this, updated version.

However, something has happened in the past couple of weeks. Now this machine NEVER runs cooler than 130F, and right now, with just Safari open on this site, typing this in, it's bouncing around between 145-165F.

Yes, I've reset the SMC. No effect.

The only thing I consistently see in the activity monitor (besides Safari) is WindowServer. I don't ever remember this being a thing there. I'm almost always in clamshell mode, connected to a 4K monitor via a Thunderbolt/USB-C cable. None of this has changed for 6 years, so it can't be the problem, but I note it for completeness.

I have the Vega 20 video option. It's my understanding that, on power, it should be running all the time. There's literally no reason that a card like that should be straining just doing simple web browsing.

After lunch, today, the computer should have been asleep and stone cold. But it was warm to the touch when I woke it up, and it was running at 170F. There was nothing running at the top of the activity monitor that would give me pause.

Has something changed recently in the OS? I can't account for this, and it's REALLY bothering me. There doesn't seem to be any reason for this change, and I'm tired of hearing the fans run already.