There will of course be some impact, but not enough to hurt the Switch. If the Switch's sales take a big hit in the middle of its life to late life, it won't be because of PS5 and XSX.
Switch is in a very interesting spot that it's in the middle of its life when the competition launches their next-gen hardware. I know Switch isn't a direct competitor, but it's still somewhat of a competitor due to being a video game platform that can act as a home console.
We'll likely get Switch 2 (or whatever it will be) in 2023 or 2024 which will be the middle of the life of PS5 and XSX. It will be interesting to see how their sales are impacted then, and how Nintendo's are.
Lifetime Sales Predictions
Switch: 161 million (was 73 million, then 96 million, then 113 million, then 125 million, then 144 million, then 151 million, then 156 million)
PS5: 122 million (was 105 million, then 115 million) Xbox Series X/S: 38 million (was 60 million, then 67 million, then 57 million. then 48 million. then 40 million)
Switch 2: 120 million (was 116 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
