2-3 second lag between changing brushes

I've had Painter 2020 installed for some time, but only just got around to using it.  I used to use Painter a lot (I have been a beta tester for it way in the past), have had it since Painter 8 - anyway.   However, for me there is a very annoying lag between changing brushes/tools.  I've tested my other versions installed 2017-2019 and whilst they have a little pause, it's not the 2-3 second gap that version 2020 has.  This is very distracting using the keyboard short cuts B and N to go between the brush and the eraser.  It really disrupts the process.

This is incredibly annoying and makes me want to give Painter up for good.  I've seen a few other posts about a switch lag (not version 2020 I note), and the only solution was to reinstall Windows 10.   Which I am NOT going to do.  My graphics card does not have AVX2, but as I'm only trying to use simple brushes I don't think this should have any affect.  I've tried all the tweaks I can, but with no effect.

Any advice, or suggestions?