Monitoring recording with TBProAudio mvMeter2 (VU meter)

but I can’t figure out how to make it work while I record.

Does Audacity support plugins whilst recording?
I don’t think so.

Also does anyone know how to resize it - it’s a bit big?

Never been able to resize any plugin on Audacity.

EDIT:

I see you are on Win 10.
Also, be aware of the other problem I wrote about here:

I suspect it will affect that plugin as well, so the readings you get whilst playing, will be too high.

Perhaps it’s better to create a “virtual cable”, then monitor that with a stand alone level meter (.exe and not .dll).
Audacity can then be used to record form the “virtual cable”.

Here is one possibility: