I think its gonna do a bit less than PS4 did around launch(~1 year), but catch up with strong midgen(second/third year).
After that i dont really know, since by then Streaming services+the infrastructure to support them might be strong enough actually affect console sales, while mobile gaming might have come far enough to even appeal to that ever crucial demographic that tends to buy consoles only late gen when its mature and cheap.
The reason for the lower start is imo PS5 will have much more competition, on several fronts.
In the traditional MS/XB markets(so mostly USA) they will have to face a much stronger XB in both message, marketing and focus.
In the regions that are usualy PS dominated, i think they will face the same issue apple is now facing, being that PS4/PS4 Pro are so good and popular that less people will upgrade like they did from PS3 to PS4.
I think there PS5 will compete with PS4 still being good for many, and even for the people that do want to upgrade from their base PS4, PS5 will have to compete with PS4 Pro.
Then there is Japan, where it is incredibly likely that PS5 will perform worse than PS4, even if it does better worldwide.
Japan has been moving away from Home consoles for a long time, and with Nintendo now having combined their Software that dominates the Japanese SW market( for example,of the combined million seller SW total 76% came from Nintendo/TPC and that does not even include SW on Nintendo systems that is not Nintendo/TPC published) with the portable Hardware that rules Japan, PS5 has much more competition than the PS4 had with the failure that was WiiU, and the 3DS that dominated HW, but didnt have the juice to run anything even remotely high end.
I hope PS5 can grow beyond PS4, but PS4 was really successfull this gen( and i say that as someone from a country that usualy has like 80% of sales being from Sony). From my personal experience, i have several friends and family members who dont really follow gaming that much, but have a ps4, who got the info about PS5 from me tell me that they dont really see the need for a PS5, since their PS4 is still great for them.
But i personally have gotten back into gaming a lot in the recent years, and i think i might pick up a PS5, even though my last home console(i dont really consider Switch one since it essentialy replaced my 3DS) was the XB360, so maybe there is indeed growth to be had for PS5.
Were heading into a recession so no. I wholly expect this to be a gen just like gen 7 where everyone struggles and no one sans Nintendo cracks 100 million.
Gen 7 had a recession, but was the most successfull generation for literally every console/handheld manufacturer.
MS sold more consoles than OG XB and XB1 combined.
Sony sold more consoles/handhelds combined than any other generation(unless PS4+Vita somehow sells another 50m before the generation ends).
Nintendo sold 250m devices, more than any manufacturer ever did(and probably will).