Hey Marte!
Glad you're enjoying your time with AHITR but also sorry to hear about the laggy playback.
While in-game you can try pressing "Shift + G" to bring up a render window and try switching to "ANGLE2" and restart the game. See if that helps. Ultimately, this is mostly a Renpy and sometimes a CPU issue and unfortunately, outside of our control.
If you're digging through the web, you might have some luck looking around for "Renpy video lag" or "Renpy animation lag" topics.
Best of luck with everything though!