If this has only just happened since you updated to the latest eM Client version, then could be the installation possibly didn’t go quite right, or something happened to your database when it upgraded, or possible some external background program is interfering or possibly is overclocking.
So first if you haven’t already “try shutdown and reboot your computer” and see if that fixes it. Sometimes that can fix OS program freezing.
If rebooting makes no difference, then “close eM Client” and then uninstall eM Client, and if you have Windows “don’t delete the database” when asked on the uninstall wizard”. Then reinstall either from the Release History Page Pc / Mac or Windows Store “depending on where you originally installed it from” and see if that fixes it.
If uninstalling and reinstalling makes no difference then if you have been making regular eM Client backups either manually via the Menu or automatically via the Settings, then suggest next to “try restoring a recent backup when you know it wasn’t freezing” via “Menu / File / Restore” and see if that fixes the problem.
If you don’t have any recent dated backups or you do but restoring made no difference, then suggest next as you have an IMAP account to go to “Menu / Accounts” and “remove and readd your account” and see if that fixes it.
If removing and readding your IMAP account still freezes suggest next to “close eM Client” and go to the following hidden database folder and “rename it” to eg: eM Client-Old. Then reopen eM Client and setup as new and see if a new database fixes it. If a new database then fixes it, make a manual backup via “Menu / Backup”.
(Hidden database folder Windows)
C:\Users%username%\AppData\Roaming\eM Client
(Hidden database folder Mac)
/Users/User Name/Library/Application Support/eM Client
If however creating a new database still freezes, then if you have any eg: optionally installed Firewall / Security programs, or optionally installed Antivirus programs or Vpns “other than what comes default with your OS” then try completely disabling those to test incase of Interference.
If you don’t have anything optionally installed like the above or you do but disabling makes no difference, then “make sure you have the latest Win 10/11 or latest Mac updates” as could be something old / outdated in the OS causing the Mail client to freeze and might need updating. There has been a lot of OS updates lately for both platforms.
Lastly freezes in eM Client “for some users” have been sometimes found to be caused by eg: CPU overclocking and / or GPU overclocking. So if you do have overclocking enabled for either if you are a Gamer, “try resetting back to default speed” and see if that fixes the freezing issue.