In my Gmail account, only a very small portion of the existing emails is being downloaded.
If all your emails are showing ok online via webmail. then sounds like eM Client has got out of sync with your online Gmail account and needs repairing which clears the local cache in eM Client and starts downloading new again.
If you have a Gmail IMAP setup, right click on “All Mail” folder under your Gmail account, and then click “Properties” at the bottom. Then click the “Repair” tab at the top and click “Repair”.
Once the repair is complete, your messages may take time to all re-appear depending on the size of your online mailbox, and your messages will be slower to read till fully cached again.
Next if the Repair makes no difference, then make a backup of eM Client via “Menu / Backup”. You can see when the backup is completed in “Show Operations” via the dropdown on the right of “Refresh”
Then click “Menu / Accounts” and remove and re-add your Gmail account via the “Automatic Account Wizard” at the top for eM Client with Google Workspace which should then fix it.
Lastly if you remove and re-add your Gmail account and you are still not seeing all your email, see my post below on how to adjust the account synching limit in eM Client and adjust your Gmail account message synching limit online.