You haven't updated Quicken since R 45.21 was released last year in December. I recommend you update the software to the latest available patch level. Download and install the latest Mondo Patch file from https://www.quicken.com/support/update-and-mondo-patch-20182019-release-quicken-windows-subscription-product to ensure your Quicken software is up to date and correctly installed.
Windows 11 running on an 8GB system might be cutting it a little fine. If you can, consider upgrading your RAM to 12GB or more. While Quicken is running, together with all your other usual applications, what does Windows Task Manager say about % Memory usage and % Disk activity on your C: - drive? Greater 80% Memory usage? C: - drive 100% busy for extended periods of time?
1) Are you Syncing to Mobile/Web? AND 2) do you actually use the Mobile app on your smartphone or the Quicken on the Web browser-based app?
The Sync process has been suspected of a number of weird happenings with Quicken. Could your problem be caused by Sync?
If you answer "yes" to the 1st question and "no" to the 2nd question, turn Sync off completely. You don't need it. The Sync process should only be used in conjunction with the Quicken app for Smartphones or the Quicken on the Web browser app. It cannot be used as a replacement for backing up and restoring your Quicken data file.
If you answer "yes" to both questions, try to Reset Sync so that the current cloud sync file is replaced with a fresh complete copy Do note that a full Sync process may take many minutes to complete.
How to reset Sync to Cloud
How to turn off Sync to Cloud for the current data file
