I noticed that in Windows 11, my RAM disk occasionally gets "full" with left over files that do not exist. It shows as almost full in Windows explorer and allows no more storage, but there are no files in it. The only solution at this point is to unmount and remount the disk.
Although it is probably not SoftPerfect RAM Disk problem, because I have exactly the same issue in ImDisk software.
RAM disk is merely a block storage, like a regular disk drive. I contains what the system puts there; no more, no less.
If you have a full disk issue, it's something to do with the file system. Usually it's hidden files and folders that aren't shown in Windows Explorer. It could also be NTFS metadata that takes up the space.
You could try using a tool like WinDirStat to find out what's taking the space, or running chkdsk.exe in a command prompt, or using exFAT as it's doesn't keep as much metadata as NTFS does.