I recently had a problem with 2 PCs which appeared to be configured identically, but whilst one would play a FLV downloaded from youtube, the other would fail. Some other FLVs played OK on both systems. After much further investigation I discovered that the activeX version of flash player on 1 of the PC’s was up-to-date, but on the other was not.
Both PCs have firefox as the main browser and the firefox plugin was up-to-date on both, but it appears that an up-to-date version of the IE activeX plugin is required for 3rd party programs like Real Player. Updating the active‑X fixed video playback
“Hi James I realise it has been a long while, but I just checked this on windows 11 (build 23H2)…”