lets say it's at 107 million this year(so 18 million for the second half of the year), next year it's unlikely to fall below 23 million with Splatoon 3, Breath of the Wild Sequel, Open World Pokemon - so we are looking at 130 million end of 2022. Even if a successor is launched at the end of 2023 I can see it surpassing 150 million, if a Successor launches after 2024 than its likely above 160 million. It all depends on what exactly are the plans for Nintendo - if it makes sense to prolong the life of the Switch until 2025 when they can offer something comparable to XSS performance on a handheld while still making a profit on hardware, I can see it trying to prolong the Switch until late 2024 early 2025.
So far they've launched a dock-less Switch - the Switch Lite, so the next possible iteration is a TV only Switch that acts as a supplementary computing & docking for Lites/OG/OLED Switches. Nintendo are already developing in a scalable way, that allows them to easily bump up resolution & fps on major titles, while it would be up to 3rd Parties to decide if it makes financial sense to update their existing games or leverage this option for future titles. This is how I think they can prolong the Switch's life and approach a crazy figure like 170 million. Basically the only chances of this happening is Switch 2 doesn't launch until 2025 and a Switch Pro is actually a complementary device that on it's own is just a TV only console with an empty Dock.