The \AppData\Local\Temp location is the system default TEMP and TMP location for Windows 11 and is what Pegasus Mail uses if not otherwise specified in PMAIL.INI. The Help > About > Info button will tells what the environment variables are set to but not what Pegasus Mail is actually using as its temp location. I have suggested that it be included if possible.
As for -ROAM, no, you don't need to be using it.
I have not seen any other report of insufficient space warnings by 4.81 so I don't think it was ever on David Harris's radar to fix. I'm fascinated by this issue though because I can not upgrade to the latest IERenderer (2.7.2.6) using its installer because it abends due to being unable to read the registry entries it checks. The installer for 2.7.2.4 still works fine. AFAIK, I'm the only person with this problem. I do not have any doubt that the issue is with my system but am clueless why. Speaking of IER, @meska , have you updated? Also know that IER has a location for its image cache. You can see its path in IER configuration. FWIW, I use C:\Temp\PMail and C:\Temp\IERCache for temp locations.