There were a lot of tutorials on how to mod PayDay 3 for the Epic or Steam versions. From the commentary I saw, there were a lot of people saying that the Game Pass/Microsoft Store/UWP version could not be modded. I found a bit of a workaround to allow you to mod it just the same as all of the other versions.
Finding the PayDay Directory:
Open up a new Command Prompt as Administrator (normal user won’t work) Navigate to cd <DRIVE WHERE PD3 GamePass is Installed>:\WindowsApps in my case this was D:\WindowsApps type in dir
You should get an example that looks similar to this:
10/16/2023 08:50 AM <JUNCTION> DeepSilver.39921928C90D0_1.0.8.0_x64__hmv7qcest37me
Take note of this directory name, you will need it for later Open a new File Explorer and put in the path that you found earlier in my case it was D:\WindowsApps\DeepSilver.39921928C90D0_1.0.8.0_x64__hmv7qcest37me
Creating the Mods Folder:
You should see the Engine, PAYDAY3 folder in there Navigate to Content\Paks as you normally would for Steam/Epic versions, create the ~mods folder and insert your mods like normal
Creating the Launch Shortcut:
Next go up 2 directories, and enter the Binaries\WinGDK directory, so for me this is D:\WindowsApps\DeepSilver.39921928C90D0_1.0.8.0_x64__hmv7qcest37me\PAYDAY3\Binaries\WinGDK
Right Click and drag and drop on your desktop the PAYDAY3Client-WinGDK-Shipping.exe and create a new shortcut via Create Shortcut Here
Right click on the shortcut -> Properties, at the end of the Target: path add a space and -openfilelog
Double click the shortcut and PD3 should open, this is what mine looks like for example (the dx11 flag can be ignored, I have it for preventing crashing reasons) D:\WindowsApps\DeepSilver.39921928C90D0_1.0.8.0_x64__hmv7qcest37me\PAYDAY3\Binaries\WinGDK\PAYDAY3Client-WinGDK-Shipping.exe -dx11 -fileopenlog
Enjoy 