Thanks!

The button is visible when I start a new game, so it probably is caused by something like that. (I'm discussing another problem with one of the mod authors right now, so it may be connected to that particular problem as well.)

I have tried disabling as many mods as I can, but they are necessary for ...

I seem to have lost my Research button. It's there again, if I start a new game, but it's disappeared from the screen for this game:

https://drive.google.com/file/d/1ALcfTLZuXik69XnR9u5XkABUI3cWyfjw/view?usp=sharing

I've tried resetting everything in the Settings dialog, swapping into and out of ...