Please verify this:
In Windows Control Panel / System / Advanced System Settings / Environment Variables ensure that both the TEMP and TMP variables point to a valid and existing folder, typically C:\Windows\Temp or C:\Users\your_username_here\AppData\Local\Temp If they point to an incorrect or non-existent folder or drive change both variables to an existing folder on C:\ (or create one) e.g., C:\Temp, and reboot Windows.
If the Temp folder is located on a too-small SSD C: - drive and you have an internal standard hard disk, too, move the Temp folder to the internal hard disk and change the TEMP and TMP variables If the folder exists … does your Windows User Account have proper access rights to this folder? If Quicken cannot create and use temporary files, all sorts of malfunctions will occur. If the Temp folder is full of junk, clean it out. Delete all files and subfolders within the Temp folder structure that Windows allows you to delete. You may have to skip a few that are actively in use.
Make sure that files in the Temp folder are NOT accessed by cloud backup software at all.
Run CHKDSK C: /r on your C: - drive (or perform Error Checking from Windows File Explorer, Properties, Tools tab).