Came here to also post an observation but this seems related so I'll post here too.
I use a Streamdeck to monitor trim values, which saves mousing down to look all the time.
I use (A:ELEVATOR TRIM POSITION,DEGREES)
I have noticed the following on the Bonanza TC
The plane loads in with my Streamdeck showing 0 degrees elevator trim
If I enable Settings > Flight Interface > Instrument Tooltips - that also confirms 0.0 degrees
On the aircrafts trim markers, its showing around -1.5 degrees (the first D below 0)
Moving the trim to 0 on the aircraft trim marker is showing me +2.1 degrees from the sim
I can see the plane marker ranges from -15 to +15 ish and the sim is -20 to +20 degrees, so I would not expect the numbers to be perfectly align.
However the fact that 0 is not 0 did throw me off.
If I bind a button to "0 (>A:ELEVATOR TRIM POSITION, NUMBER)" it will reset as above - sim showing 0, trim marker at -1.5.
So this would explain why when the OP sets their trim to 0 is getting a +2 degree climb
Maybe this is how the aircraft really is??