New to this forum and with recent hardware upgrade moved to Adobe Subscription so new to LRc. I ran into the above OP issue, suddenly, after work fine till today. I got the volume does not support trash notice. I tried all the suggestions on different sites given in an internet search on the topic. Not thing worked so I tested deleting unwanted files from the volume in question directly from Finder, and it worked fine....so no it is not an OS, formatting, permissions. or disk full problem - for me, as none applied. After trashing the files I went into the same folder within Lightroom and after moving to the said files in the catalog it gave me the expected File not found in develop mode. So I highlighted those files and clicked remove from "Lightroom". After this I tried to delete other files with the option "Remove from Lightroom and Delete from disk".......and all is working as expected again, file were moved to trash and then i emptied from the trash. This got everything working again, no warning message. For me but I don't know if it is a lasting solution. From my opinion, with computer experience including professional since 1982 it "appears" to be a Lightroom problem given my tests and results.