Good day, yes I myself try to do this kind of simple editing in online Reverser, I for example have already found one. I also needed it to be fast, because I make several videos a day and don't have time to run heavy editors. I found here https://www.fastreel.com/reverse-video.html such a reverter and it works so far without any errors, and very fast because it is online.
I do a lot of video editing myself, but I've been needing to flip videos upside down a lot lately. And to do it in a computer program is not rational, it is very long and slow. Is there any way to flip online quickly?