Who says you need to upgrade monitor for PS5? It supports 1080p 60 Hz perfectly fine, in fact most games run around 1080p when in Performance mode, and those that render higher res will give you free supersampling on that monitor.
PS4 and Xbox One were outdated and underpowered already on release, I wouldn't bother with them when you can play the same games on PS5 usually with better performance and/or graphics