Short answer is I don't know beyond I think you're fine for any 16-21-24MP designs. And plenty argue 21-24MP is where most should probably stop. Now I'm going to blab.
In the Fuji world some people argue the 16 to 24 jump was when things went from analog to digital looking and argue there are downsides of even that high. Some systems change mounts enough you kinda can use it as a division (harder to do for Nikon's long compatibility back). The 16-24 designs probably start to breakdown around 40MP+ (a guess, because honestly I haven't tested to even state that - besides examples I mention), but can be a solution until you pick up "native" glass for a new resolution. Watching others debates are often a clue. When the GFX system was announced lots of people, including myself, used Mamiya M645 medium format glass. It looks great... until you compare to native GF lenses. Damn! Over time hardly anyone uses M645 lenses (unless you want character - say funky, busy bokeh). That said many still use some EF lenses and others use Sigma Art lenses to fill in focal lengths, and I bet they outperform the M645 glass (on GFX), and they're happy.
Half this is like TV shopping. One looks incredible, then you glance at the colors and blacks of the model next to it. And then all the other questions - is a "portrait lens" more suitable over time than one used for landscape? Maybe. Should you consider buying new lenses if considering a doubling of resolution new body? Maybe... if perceptual resolution is the goal. The reverse question - should you stop climbing resolution if you have lenses you know and love? Maybe. Whatever the end point, does every lens eventually become a character lens? Maybe. Seems so for a ton of big cinematographers. Does sharpness/resolution over time stop being a primary goal? Also seems so for many.
I'm babbling and not really answering your question, because I just don't know, but to make things even more confusing there are long term medium format film shooters that claim digital starting beating traditional MF by most measures with Micro 4/3s around 2010. If true, we're a dozen years into everything equal or larger sensor and equal or higher resolution being icing. So whatcha gonna do with that? I know it's not a very Head-Case question, but gear in the way? 🥴
EDIT: Just reread the above. Boy that’s a lot of useless text.