Dear Jo_1922,
Glad to see you in Microsoft Community.
The WDI folder should store event traces related to boot/logon/logoff/shutdown. Some of the earlier files in these folders should be deleted automatically.
They may not be deleted automatically due to a three-party program or for some system reason, but you can delete them manually. If you can't delete them, please do this in safe mode.
To enter safe mode, you can refer to this:
- Press Windows logo key +Ion your keyboard to open Settings. If that doesn't work, select theStartbutton, then selectSettings*.*
- SelectUpdate & Security*>Recovery.* Open Recovery Settings
- UnderAdvanced startup*, selectRestart now.*
- After your PC restarts to theChoose an optionscreen, selectTroubleshoot*>Advanced options>Startup Settings>Restart. You may be asked to enter your*BitLocker recovery key.

- After your PC restarts, you'll see a list of options. Select4or pressF4to start your PC in Safe Mode. Or if you'll need to use the internet, select5or pressF5for Safe Mode with Networking.
About the slow boot of SSD.
I think you can prioritize turning off some boot-up items. Then clean up files to make sure SSD space remaining available is more than 25%
To clean up the disk, right click on the partition in File Explorer - Properties - Disk Cleanup - check all files and clean up (make sure there are no important files in the Recycle Bin)
Then go back to Disk Cleanup - Clean up system files - check all files and clean up again
If there is anything not clear, please do not hesitate to let me know.
Kirk | Microsoft Community Support Specialist