I ran into this a while back.
It’s not new
It’s not specific to Pixel photos.
The app and cloud service just don’t have support for modifying the EXIF tags, so if *any* camera has added GPS data, you can’t use Google Photos to change or remove it.
The estimated location is stored in the Google Photos database and can be modified within the app.
You *can* turn GPS off in the camera app.
A few months ago I dug into ways to work around this with photos that had already been taken with the GPS coordinates. Annoyingly, you mostly have to save the photo, remove the tag, and re-upload it.
https://hyperborea.org/tech-tips/gps-remove/
(I take a lot of photos for iNaturalist and reference photos for OpenStreetMap editing, so I’m constantly turning GPS on for those, and then back off for personal photos, and sometimes I forget.)