There should be no performance difference between 3.2 and 3.3, but indeed, there is a big difference in startup time with MDL versus without.
If you are seeing something other than just that, we would need you to attach the score you are problems with and gives us precise instructions to reproduce the slowness you are seeing.
Comments
What is slow, working with it or loading it the first time? If the latter: do you have the MDL extension installed? Of so, this is quite normal.
You get 3.2.3 (and all other older versions) from the download page, https://musescore.org/en/download#Older-and-unsupported-versions
There should be no performance difference between 3.2 and 3.3, but indeed, there is a big difference in startup time with MDL versus without.
If you are seeing something other than just that, we would need you to attach the score you are problems with and gives us precise instructions to reproduce the slowness you are seeing.