Hi there.

I installed the game on my new desktop. Now I have the problem that whenever I zoom out using the middle mouse button or the keyboard, the game zooms out extremely slow. But when I zoom in or rotate with the mouse everything works perfect and smooth.

Any fixes? Can't find anything online and I also cant think of a mod causing this problem.

Temporarily remove all mods, just to confirm.

If the issue persists, check the scrolling behaviour in another application to test if it's the mouse itself that could be faulty.

This could be due to the performance issues, which Sims 3 is famous with and it's poor optimization.
https://simswiki.info/wiki.php?titl..._Address_Aware.

It does this with and without mods. The scrolling works fine on internet or other games.

Also try using LD's Smooth Patch in case you don't have it. Right now is labeled as "unsupported" here at MTS, but it still works perfectly fine.

If it were performance related, you'd likely see the issue come and go as performance fluctuated.
You could try a lite world like Builder's Island to rule this out.

The MTS Smooth Patch is unsupported because it was superseded by Sims 3 Settings Setter, which includes an improved version of the patch.
S3SS does contain some patches that improve camera movement, so they may help alleviate the issue - though it would still be useful to identify why the issue is happening in the first place.

Thanks for enlighten me - I was just wondering in what s3ss is better than smooth patch! I will try it myself now.

Maybe we will find the reason for the issue if OP shares their mod list, if removing them doesn't work and it's not performance related.