That will be the storage on one of your accounts is 82% full, not Thunderbird.

Recently i have seen a lot of folks that store photos on googles drive getting issues with their google storage getting quite full as Google do not offer a separate allocation of space for mail and "other stuff', it is all in the same space allocation of 15Gb.

That doesn't really make sense. What are you observing that makes you think you have "82% full of your Thunderbird email program"?

Is the problem that you have too much mail stored on the server and you don't know how to remove it from there? What type of mail account is this (POP, IMAP)?

If 82% of your server storage is full and you want to know how to free space, delete messages and/or move messages to local folders. You could also ask your e-mail service provider if your storage space on the server can be increased.

If you are talking about google/gmail - good info here explaining that the 82% is not just emails: https://support.google.com/mail/answer/9312312

When you 'delete' emails please make sure they go into the gmail imap Trash' folder, then gmail will auto remove them after they have been in the Trash for 30 days. If they do not go into the gmail 'Trash' then gmail thinks you mean only remove the 'label' meaning you still have the emails archived in the 'All Mail' folder using up space.