Guys: I was having problems getting the pop-up windows (Payload Manager, etc.) to show, and here's how I solved it - permanently.
I have a rather ambitious setup, with three 65" LG Oled monitors driven by a single GTX 2080 Super for the outside view (65 deg offsets), plus two smaller (26" and 22") touch-sensitives driven by a GTX 1650 for Air Manager. Though the LG's are 3840x2160 native (or 4096x2160, depending on who you ask...) I run them at 1920x1080 to get a respectable 40+ fps with textures at max (I found that is my personal key graphic parameter). Try that at higher reses and you run out of graphic memory (!) I have the C-172 and the C-T210M running like a charm (two charms...) with the Brunner yoke and rudder making the experience un-freakin' belivable (I fly a P46T in real life).
Then I installed the TBM900 and, like you, could not get ANY of the pop-up windows to show: the left-hand hiding selection buttons did (e.g. I could get the GPU) but not Payload Manager etc. After a lot, and I mean A LOT of trial and error, this is what worked for me:
1. In Windows, disable ALL THE DISPLAYS EXCEPT ONE (I chose to remain with a single 65" LG). Start the sim (11.50 with Vulkan enabled - what a difference in fps!), go to graphics preferences, and select "display default" as the resolution of the one and only X-Plane display. DO NOT SELECT THE ACTUAL RESOLUTION (in my case 1920x1080 - I'm not sure if this is necessary, but "display default" sure works for me).
2. On that single-display, cleanly-defined resolution setup, check that you can open all the TBM pop-up windows, and that they all FIT NICELY WITHIN THE DISPLAY. If not, shut down and restart X-plane (I even shut down and restarted the computer several times during the process, to make sure I had "fresh" set-up data each time).
3. Gradually re-enable the other displays in Windows and the respective screens in X-Plane (maybe you can do all of that in one step, but by doing it one screen at a time, I got the whole thing to work). Check that the pop-ups are still there and are the right size. Done!
I think what happened is that when I first fired the TBM900 with my existing configuration, where I had been experimenting with higher resolutions (ran out of Graphic VRAM) I must have left a hornet's nest of X-Plane and Vulkan settings that confused the TBM when it first started, and sent the pop-up windows to never-never graphics land.
Anyway, so far so good. A couple more notes on using the TBM900: I very highly recommend Ch. Cole's mixture.lua FlyWithLua script. Works like a charm and is actually very realistic, especially in combination with a home-made (3D printed) throttle "gate" on my GoFlight throttle quadrant.
Now, if I could just find the correct commands to clear the master warning/caution indicators... the "tbm900/lights/cas/master_caut" dataref mentioned in the DataRefs+Commands.txt file that came with the airplane (and companion _warn) seem to work OK, but the COMMAND "sim/annunciator/clear_master_warning" (notice it's a "sim/" command, not a "tbm900/" command) doesn't do squat. So I cannot clear the masters from Air Manager. Ideas, anyone?
Antonio