Man utd actually spent 50m on a 20s full back

I think you may be mistaken!

Manchester United did not spend £50m on a full-back from the 1920s. In fact, the concept of a £50m transfer fee didn't even exist until many decades later.

The 1920s were a time when football was still a relatively amateur sport, and transfer fees were much lower. Players were often transferred between clubs for a few hundred pounds or even just a few pounds.

Manchester United has made many significant signings over the years, but none of them were from the 1920s or cost £50m. If you're thinking of a specific player, I'd be happy to try and help you identify who it might be!