See https://support.mozilla.org/en-US/kb/compacting-folders#w_potential-complications Please read https://support.mozilla.org/en-US/kb/compacting-folders-potential-complications

Once we are on the same page about the fact there is no uncompact please post what it is you are looking for someone to help you do.

I am aware what compact does and I read this article before I did it. I am using Thunderbird for 10 years now. I am always cautious about compact and try to avoid using it but it started to slow down. That's why I used it and I made sure that no antivirus tool interfered. The Repair feature does not work because it tries to connect with the email server. It is an old offline account. Any hint where I can find my emails (Inbox, sent) and make them visible in Thunderbird again?

Update: I used Everything to search for my inbox files. I found several inbox files. Please note that I have several email accounts. Can someone please show a way how to identify which inbox file belongs to a specific email address? For example: 4 different ones, such as imap.zoho.com, imap.zoho-1.com, imap.zoho-2.com, imap.zoho-3.com. Instead using the trial and error method, it would be great to be able to identify it beforehand; in order to avoid any additional complications with my inboxes in Thunderbird.

Lets go way back here. I have used compact regularly for decades now without issue. Compact has over the years had some bugs, but they have been few and far between really as regards to data-loss. User ignorance and assumption have seen a lot of apparent data-loss attributed to compact and this is yet another example. An imap account is synchronized, even when the server account is closed.

So we are looking for deleted mail post compact. I do not hold much hope at all because you are looking for deleted mail post the process that removes deleted mail from the storage folder. Go to the account settings in Thunderbird. on the first screen of server settings for the account it shows the local directory used by that account. Then once you have the correct folder open the inbox file (no extension) in a text editor. Does it contain anything?

As an aside, unless you have multiple account on zoho it may be worth looking in all of them as you used imap and may have reinstalled the account over the years and the residual mail may still be in those folders if the account was removed from Thunderbird.