deleted email has now vanished, and so has the 'trash' folder . . .

Slightly odd bug (or maybe / probably, user error?) in Mail v16 (running—slow to upgrade here—OS 15.2 on Mac Studio circa 2022):

I have an archived email account, in Apple Mail, meaning it's not connected to the internet or any active mail server. Occasionally, I need to reference email from this period, which I do by launching Mail. Today, while looking for something else, I accidentally deleted an email (it's as easy to do as an inadvertent mouse swipe).

When I went to search for and retrieve the email in the 'deleted emails' folder, I found nothing in the folder. Nor, in my sidebar, is there a 'trash' folder to search within. Went down a lot of rabbit holes / forums seeing about ways to re-instate the trash folder, and I've tried hovering over the favorites '+' sign etc., but no option to add the trash folder, and mysteriously the email seems to have disappeared into thin air.

I've always been perplexed by the file structure of mail, so much so that drilling down into its respective folders within the finder only leads to a sort of existential peril. But I did try that too, to no avail. I have a feeling my situation is complicated by the fact that this is not a live account; but still, hopefully, there exists a solve.

Is my email gone for good? I feel like it's just hidden in either the 'deleted messages' or the 'trash' folder (and maybe, in the latter case, the trash folder is hidden). Any ideas heartily welcome. thanks!