There is clearly mistreatment of prisoners of war going on in this war. That is clear. I think it is necessary to point out that it is happening on both sides.
A month ago, a video came to light showing Ukrainian soldiers murdering Russian prisoners of war. Even though, as we've had pointed out, a video only isn't proof per se, the BBC was able to verify this by geolocating where this happened, which was in Ukrainian-held territory. The Guardian newspaper reported that bodies were spotted in the area by satellites, so it does seem likely that in this case, the Ukrainian soldiers murdered Russian prisoners. There have actually been more than one such video. There have been a substantial number of videos not just of the murder of Russian prisoners, but also of the beating of Russian prisoners and the desecration of dead bodies, so there have been, I'm afraid to say, multiple violations of human rights on both sides in this war.