Re: MPLAB X IDE v5.40 for Windows 10 is running slower and slower
A restart of MPLAB X often helps a bit.
If it happens more regular, you could try to delete the "cache directory". This thing often is growing and growing and growing. To my experience a few hundred MB are quite normal, but you may also find it with more than several GB.
Look up the path in MPLAB X in menu "Help", "About". With Windows it is probably something like:
Close MPLAB X, and wait till it is done. Then delete the "var" directory. Then restart MPLAB X.
But I'm still working with v5.25 and also I only have 2 different projects which I open regularly.