Ever since upgrading to SketchUp 2023 from 2022, our vertical tray size will not save as a preference. Every time I launch SketchUp now, I have to manually resize all my trays to my monitor size…
This sounds like evidence that SketchUp doesn’t have permissions to write the required files that save those settings. Close SketchUp, find the downloaded installer file, right click on it, choose Run as administrator and then Repair. Reboot the computer, open SketchUp and make the changes. Then save a model file and quit SketchUp. See if your adjustments carry over.
Thanks for the help! Before I do that, I should mention that it does remember other customizations like tool bar visibility and locations, and even which trays I have visible. Does that change the recommendation?
Nope. Doesn’t change it a bit.
Doing this won’t hurt anything.
Thank for the suggestion. Unfortunately, it did not fix the issue.
SketchUp, please fix this. In our line of work we open and close different SketchUp files dozens of times a day. Having to resize each tray in each session is really annoying redundant activity that should not have to be done. I cuss the SketchUp name everyday multiple times because of it.
And also please fix multiple monitor support issues with disappearing dialogue boxes. For those of us that travel and work in the field, it has been an ongoing saga for years with SketchUp. we don’t have that issue with other software.
I have the same issue. My tray continues to return to the same super wide size even after I adjust it.
Close ALL SU instances. Start only ONE session and setup your tray; then close SU and restart. Does it helps? Also, you might try to run SU as Administrator
Run as Administrator does fix the issue. Unfortunately, I work for a large company (30,000+) and our IT policies simply do not allow us to have admin rights on our PC. 
This is common in large companies to try and reduce compromised systems. None of the other software we use has this issue with saving preferences or settings, just SketchUp and it only started this behavior after 2023 release.
Thanks to everyone who identified the problem!