Strangely scaled and pixelated font and buttons

I’m completely new to the world of QGIS and GIS in general. I’m going through the official training manual, and I’m having fun and everything is working out all right.

For some reason, when I got back to it today after a week or so all the fonts are strangely pixelated. Also, the buttons (and the font, I’m not sure?) in the toolbar are slightly pixelated and seem scaled up a little bit. See the screenshot.

I did switch to a different monitor, but did not change settings. In the windows display settings scaling is set to 125% as it always was – I didn’t change anything here either.
It also doesn’t go back to normal when I use my old monitor – and QGIS is the only application I’m having this problem with (thus I’m asking here and not in the superuser forum).

Any help for that?

Edit:

I’m using Windows 10.

Also, I tried exporting a map, in the resulting pdf file the font looks good and not pixelated.