I'm not sure why the forum has decided after a single football match that he can't play as a #8. The system/positioning of both Mount and Bruno against Wolves didn't work. The gap to Casemiro was too big and Casemiro himself didn't help by having a poor game (to be expected, he has been a slow starter throughout his entire career).
But Mount has undeniably played #8 a lot during his career. You can look up heat map after heat map showing a classic left-sided #8 position. And the stats from several of his best seasons reflect a midfielder producing as much defensive and offensive work. His games for England have mostly been as a #8. Yes, he has also played as a #10 and as a wide attack midfielder/winger. But at least a third, maybe closer to half, has been as a #8.