I really don't think so.
Xbox Series X seems to be learning from the Xbox One's shortcomings. Now is there a chance that Xbox Series X could be the Dreamcast of Xbox? Critically acclaimed but sells about the same or worse than its immediate predecessor which leads to the end of Xbox consoles? Yes, there is a chance. But I would say that's not the most likely outcome. And Phil Spencer said the Series X is not planned to be the last Xbox. I mean I know you don't want to admit the end before the console even releases, but he's probably right.
The PS5 won't sell as much as the PS4. And it sure as heck won't touch the PS2. But in a bad situation, PS5 will manage right around the lifetime sales of the PS3.
My relatively pessimistic prediction would be that the two combined sell 130 million. But I think they'll likely sell 145-150 million combined.
Lifetime Sales Predictions
Switch: 144 million (was 73, then 96, then 113 million, then 125 million)
PS5: 105 million Xbox Series S/X: 60 million
PS4: 120 mil (was 100 then 130 million, then 122 million) Xbox One: 51 mil (was 50 then 55 mil)
3DS: 75.5 mil (was 73, then 77 million)
"Let go your earthly tether, enter the void, empty and become wind." - Guru Laghima