It's hard to say. But if I were to give a guess I'll say it's unlikely to outsell the Switch 1. It's super difficult to reach 150M in sales for any console.
I have a feeling some Switch owners won't feel the need to upgrade if it's just a regular Switch 2 with better graphics being one of the only major improvements of the system. The Switch 1 pretty much still functions the same way as a Switch 2 would being a hybrid console and I could see some current owners being content with just sticking to Switch 1.
Regardless, if it's just a standard Switch successor it'll likely be another 100+ Million Unit success, just not outselling the Switch 1 which isn't at all a bad thing either.

I won't completely rule out the Switch 2 maybe outselling the Switch 1. I feel like the hype around the Switch 2 at launch this time around will be alot stronger that the Switch 1's hype mainly cause Nintendo is bigger than ever now after the Switch 1 lifespan compared to the 2017 launch of the Switch where Nintendo was just coming off their worst most unpopular era. So that extra launch hype surrounding a new Switch console may induce newcomers to hop on and try a Switch 2.
Also, if Switch 2 ends up having a longer life that'll certainly raise the possibility especially since I believe the Switch 1 easily has the potential of selling 165M+ if the successor isn't releasing in 2024.

A tiny portion of Switch owners preferring to stick with a Steam Deck or other PC handhelds going forward instead of getting a Switch 2 is factually going to happen so I don't get the point of your reply. The Vita obviously caused the 3DS to sell less than it otherwise would've so PC handhelds increasing in popularity will cause some people to stick to that instead of Nintendo going forward since the Switch had no real competition in the handheld space for the vast majority of its life but now there's more options.

Hmm.

Atari went from winning Gen 2 to losing badly every platform after.

NES won Gen 3, SNES won Gen 4.

PS1 won Gen 5, PS2 won Gen 6.

Wii won Gen 7.

But here comes the messy part. Switch is a hybrid and there's no clear consensus what gen it is. If it's Gen 8, it beat the PS4. But if it's Gen 9, it also is pretty much guaranteed to beat PS5. PS5 doesn't have much of a shot of selling over 130 million and forget 150 million or more. 

In the handheld space each gen, Nintendo wins each time. In home consoles, it's either Nintendo or Sony once they came on the scene.

Could Switch 2 sell less than PS5 or the future PS6? Quite possible. But there's almost no way it would be dead last. There's almost no chance Xbox ever reaches 360 levels again unless Nintendo or PlayStation are selling well too. 

Switch is a Portable console with a docking feature which tablets, laptops and phones have had for years and years.

It's technology is pure portable technology.

3DS and WiiU were 8th generation consoles, that makes the Switch a 9th generation console with 8th gen hardware capabilities and feature sets.

I don't think it'll actually have that much to do with the system as much as other factors.

Nintendo is building a compounding generational fanbase, which means it might just naturally be growing, and if their movies really take off (like more Mario CG movies, Zelda movie) that is going to propel their IP sky high like what happened with Marvel and the movies.

The nay portion would be that Nintendo tends to struggle with successor platforms. But again maybe the generational thing and the movie factor will overcome that.

My point is that it’s going to be such a minuscule amount that it will have essentially no bearing on whether or not Switch 2 outsells Switch.

Like all Nintendo hardware, Switch sold on the strength of Nintendo IP, take those away and Switch becomes a niche device so the people who bought a Switch to play Zelda or Animal Crossing or Pokemon or Mario aren’t going to skip on Switch 2 because of handheld PCs that have none of those games, cost significantly more, are way bigger and have no exclusives in general.

I wouldn’t be surprised if Steam Deck, Rog Ally & Lenovo Go sell less than 10 million combined lifetime then factor in the number of them who also end up buying Switch 2, the people who were never planning on getting Switch 2 regardless of these devices and you are left with potentially a few million who skip Switch 2 for one of these devices.

Unless Switch 2 sales end within a few million of Switch 1, for example 152 million vs 149 million, than these portable PCs are not going to be a factor in deciding if Switch 2 outsells Switch 1.

Atari 2600's successor failed, NES's succeeded. SNES's failed, PS1's succeeded. PS2's failed, Wii's failed, PS4's failed. I know people like to argue that Switch is not ninth gen, but it's simple math (it can not be the same gen as Wii U). So its competition is PS5 and Series X/S, and it's sure to beat both. 

Regardless, it's not common for one dominant home console to be followed up with another. 

No, but the Switch 3 will outsell the Switch 2 and Switch 1. 2030-2037 gonna be insane!

I said at least a few million in my first comment though so not much different than what you're saying. My point was that outselling the Switch will be so hard that PC handhelds taking only 5-10 million sales away could be enough by itself to prevent it from happening. When you're getting to peak console sales a portion that size can make a big difference in the final rankings so I do think it making the Switch 2 stop in the 140's instead of the 150's is a possibility.

I must say that i don't think so! of course it could be the next best thing but i think Ninty had many things going in their favour this generation.