Hi I would recommend to try this.
I had the same problem on the create your character. I think I fixed it. It is working for now.
First I would recommend to find the file in which the game has been installed. for me is :
C:\Program Files (x86)\Steam\steamapps\common\The Sims 2 Legacy Collection
and then do a search on the search bar with .exe and find the "Sims2ep9" or the one to start the game.
then, go to properties and change compatibility to "windows 7", I also check the "disable fullscreen optimizations" and "Run this program as an administrator", then press "apply" and follow by "ok".
I also went to setting > display > Graphics and proceed it to find the game and put it to run on the best graphics card that my laptop has. "NVIDIA" in my case. If you cannot find the game, press on "add desktop app" go to this "This PC" or wherever you got the game install and find the same file from before, when you tried to do the compatibility:
C:\Program Files (x86)\Steam\steamapps\common\The Sims 2 Legacy Collection
and then: "Sims2ep9".
add the game and make sure you select the best "GPU preference" and "optimizations for windowed games.
then (if you can start the game, in which I hope it does as it worked for me), make sure to lower the graphics to medium, everything to medium and then I think you should be fine.
Hope this helps!