Exact groups are byte-for-byte identical files, found by the library health scan, so only files it has already checked appear here. Likely groups are tagged as the same series, issue and year, or sit in one folder with names that differ only by a copy marker — they may be different scans or variants, so check before you trash. Nothing is removed unless you choose a copy to keep; the others go to the trash and can be restored.

Three ways to clear a group: Keep selected, trash the rest; Dismiss if you already sorted it out elsewhere, such as the File Manager — it stays hidden until the next library health scan and comes back only if that scan still finds it; or Not duplicates if they are different comics, which hides the group for good unless another copy turns up.