The gallery App would have been the best bet, I assume, because it should have a trash bin (can’t speak for the default gallery App though, I’m using a different one).
The file manager App seems to assume users know what they are doing when confirming delete operations, no trash bin in sight.
Since you already checked the gallery App without success, feel free to try undelete or data recovery tools, preferrably running on a computer connected to the phone using USB debugging, and preferrably not installing anything new on the phone as to not overwrite storage which might still hold deleted data (might be unavoidable, though, to an extent).
They tend to get mixed reviews, so perhaps don’t expect too much.
This is one reason i use Syncthing to sync files with my phone.
Yes it also syncs deletions, but it moves them into a separate folder (on the other device) which i can empty later, and it can even handle revisions (all by settings of course)
With the last major update to e/os v.2.6.3 there is a change. The gallery app seems to sort deleted photos into trash. But the trash folder is empty after doing so. Apparently this might have been the solution - but does not work (yet).
I heard that the problem with the non working trash folder in the standard gallery up is related only to the use of SD card, i.e. it might work on the hard disk of the phone.
Anyway, I think the trash folder is such a basic standard feature of computers and phone - the average user will rely on it. Therefore /e/ needs to have it working well.
I’d like to add important information (regarding pictures on sd card, e/os v.2.6.3 ). I “delete” them by marking as “move to deleted files” and instantly get a confirmation pop up. But, the pictures are simply not deleted nor moved to deleted files/trash. Pictures stay where they are.