Now the scrollbar is shown after applying the fix:

Compare to what happened before applying the fix:

I'm afraid this solution won't work with the next version of Cinnamon.
The CSS property max-height is deprecated.

The CSS property max-height is deprecated.

What is the alternative?

Using height, after calculating the required height. I'm running into this problem with one of my applets.

Using height, after calculating the required height. I'm running into this problem with one of my applets.

I'm afraid this solution won't work with the next version of Cinnamon. The CSS property max-height is deprecated.

Are you sure it has been deprecated? I can't find any references to that into the cinnamon code, also it seems to still be used in the codebase. I tested this with Cinnamon 6.7 on the LM 23 alfa and seems to be working as well.

I ask this because I'm planning to use max-height as well in this pr #13640 (I initially thought this PR was similar to mine, but this is directed towards the notification applet menu, while I'm handling the notification pop-up).