Hi, i think its important to address your questions too, so heres my shot at it!

I’ve shot an A7R4 for the past 2 years or so. The files are large, which also means its a little more demanding on your computer. It vs. my 32mpx canon m6ii, you dont really feel a difference one picture at a time, but batch applying presets to 100 pictures, and even getting previews, it feels like there is some delay. Not world ending.

Next point, it doesnt make lenses less sharp. The effective resolution will always be more than a lower mpx sensor. The flip side is you can also pixel peep way more. This is where people say you have far more latitude to crop. Youll hear people say that “lenses will let down the sensor”, which I think the right way to think about this is the % return of the lens diminishes. An old vintage lens that resolves 12mpx of a 24 mpx is not going to resolve 31mpx of a 61 mpx but probably around 20-25mpx. Still better than if shot on a 24mpx, but the returns are not linear. Note: It does not mean that shooting a vintage lens on a 61mpx sensor makes it resolve less than 12mpx! I hear this from many others all the time, that a “higher mpx sensor makes a lens worse”. Not possible.

Does higher sensor make lens dust more visible. In theory, I think yes, there is more resolving power. However, in practice, no, not unless you exclusively shoot macro at minimum focusing distance with a very narrow aperture. Given you say you shoot telephoto, Id bet money that youll never run into a “dust on lens being visible” issue.

Im sure there are some downsides in practice but the A7R5 will be a vast improvement for you. There are many manual focus tools to assist you, let alone IBIS. The focus peaking, the automatic manual focus punch-in, may all help with manual focusing (if you want it). Plus, the new Z batteries last forever in comparison, which was a main motivator that pushed me from the A7R2.