Open Gmail in a web browser
Go to the folder or search results containing the emails
Click the checkbox at the top left to select the visible emails
Click the blue text that says Select all conversations in this search if it appears
Click the trash icon
Repeat the process on other pages or searches if needed
Use search filters like older_than:1y, has:attachment, or from:sender@example.com to target more emails at once
Empty the Trash folder if you want to permanently delete them