Google Workspace has a 25-day admin recovery window after permanent deletion. If you're within that window there's a good chance you can get it back.
1
Log into Google Admin Console as a super admin.
2
Go to Directory > Users, find the affected user.
3
Click Restore Data, set the date range, select Gmail and click Restore.
If you're outside the 25-day window, Google Vault (if your plan includes it) may have retained a copy depending on your retention policies.
For personal Gmail accounts there's no admin recovery option once Trash is emptied. In that case a tool like SysTools Gmail Backup can help if you had previously backed up the account.