@jojochax The pink line is a known issue on ARM Macs and shouldn't have any other effects. It's just a visual bug.
The crackling happened in Sims 4 for a while, but it doesn't usually occur in Sims 3. Try using a different sound output device, for example the laptop's speakers vs. headphones connected via Bluetooth or jack.
Without mods, all I can suggest is saving often and deleting the cache files every time you quit. Sims 3 has never been completely stable, and the University world doesn't have any special errors or glitches that could be addressed. So this might be more of a question of working around the crashes rather than preventing them entirely. The cache files are in Documents > Electronic Arts > The Sims 3:
- CASPartCache.package
- compositorCache.package
- scriptCache.package
- simCompositorCache.package
- socialCache.package
If you're willing to try a few mods, it's worth installing NRaas ErrorTrap, Overwatch, Register, Traveler, and MasterController. All but the last do their work on their own and in the background, fixing issues that could lead to crashing or corruption without the player needing to do anything. MC does nothing at all unless you use it to issue a command. You can find descriptions and links here:
https://answers.ea.com/t5/Technical-Issues-PC/Sims-3-Common-Game-Fixing-Mods-Hero-Approved/m-p/9838855#M244208
If you do add the mods, try running an MC town reset: click on the map tag for the University admin building (the stand-in for City Hall here) and select NRaas > MC > Town Options > Reset Everything. This will reset your own sim too, so do it when that would be least intrusive, for example when the sim is already at home and you don't mind their mood being reset too. Then use "save as" to rename the save, quit, delete the cache files (again), and reload.