If you can’t get into eM Client as it’s crashing then sounds like your database is corrupted & either needs manually repairing or creating a new one.
So to try manually repairing your database do the following via @Gary post below from the following thread.
https://forum.emclient.com/t/em-client-stops-working-when-accessing-some-local-folders/93066/2
On a PC, close eM Client and open a Windows Command Prompt. Not a powershell, but a command prompt. Paste in this command including the leading "
“C:\Program Files (x86)\eM Client\MailClient.exe” /dbrepair
Or, on a Mac, quit eM Client and open a Terminal. Paste in this command:
/Applications/eM\ Client.app/Contents/MacOS/eM\ Client /dbrepair
When that is done, restart eM Client as see if you still have the issue.
…
Now if the manual repair makes no difference, then you will need to manually “rename the current eM Client hidden database folder” to eg: eMClient-Old and then open eM Client which will then open the automatic account wizard to setup as new.
Windows hidden eM Client database folder)
“Users\yourusername\AppData\Roaming\eM Client”
(Mac Hidden hidden eM Client database folder)
“Users\yourusername\Library\Application Support\eM Client”