So I see ads (even videos!) instead of my simple html page, or on top of it. It's terrible!
I just factory reset, then if I do the system updates from the control panel they come back. It's reproducible.
I don't install any app since I really only need the browser to display an html page from a server on my LAN.
Can't be too old as you are still getting updates.
I don't think it gets new updates, but it downloads up to the last update that they put out.
https://www.amazon.com/gp/product/B01MS6I0HQ/
This short USB power cable
https://www.amazon.com/gp/product/B092KF36T6/
This wall switch to tap USB power out of a wall switch box so there would be no visible dangling wires. This will only work if your apartment has neutral wires in the switch boxes. Older apartments often don't have them
One of the things I like about Samsung tablets is that they have a "Battery saver" feature where you can restrict it from charging the battery past 85%, which is a generally good move if your tablet is going to be permanently plugged into power and used as some sort of fixed display.
I've had MANY brand name devices with lithium batteries bulge when left constantly plugged in at 100% battery for months and don't want to risk an explosion.