Switch will be at #5 at the end of the year, and it will be at #3 sometime in 2022. It's still too early tell when (and if) it will end up passing the top 2. The contest with the top 2 is the real interesting one at this point.
As how the switch is going under 400k weekly now regularly, and going close to 350K it becomes more and more questionable how many units will sell this year.
This year it began very strong for it however with every month the sales become less and less impressive to the point where 350K was PS4 sales territory when it was peak in 2017/2018, which console had 20M peak year, therefore the potential of the switch for 30M for this year becomes more and more unbelievable, and going more like 25M. I think even if the PS5 and XBSX get better stock by the end of the year this also could take some effect on the switch sales, because I am sure now since the launch of those consoles switch gained some new sales because of the hard to find Xbox and PS consoles, cuz some people that want to buy something to play they can't find PS5 or xbox and they take switch.
Also see the previous gen, 3DS was doing 13 and 14M per year and in 2014, when PS4 and XB1 got more in stock, the 3DS fell to only 8M for the year. Big drop.
Once the PS5 and XBSX got in full stock switch will drop to probably 200-250K per week.
So it is more like 50/50 if it will reach #3 by end of this year.
And together with the expected switch decline for the next year, switch may do something like 15M next year, so it's not also sure 100% if it will pass PS4 by end of 2022 (which should be around 117M-118M by this time)
Also with the disappointing OLED model revealed, as anyone was waiting for the Switch Pro, now surely the sales won't pick up, as they would if there was real Pro model. One more reason why Switch will probably not make more than 25M this year. And also one more reason why Nintendo may launch the successor sooner than expected.
So basically you are showing one good way the sales for the system can happen, I will show one other not so good way (but pretty realistic one).
by end of 2021 - 100/102M
by end of 2022 - 115M
After this it is too difficult to predict, cuz they may launch successor after which point switch will just fall of a cliff. just like pretty much every console did in the last few generations, and switch will make no more than 10M total after the successor launch. (and as there are rumors that this Pro model now will become Switch 2 there is a good chance they will not wait much, more like 2023 launch)
However if they wait till 2024 switch may reach 125-130M total lifetime, which is still impressive however far far away from the #2 or #1 selling console.
And I will just give an example for every optimist here, with the PS4, they are different consoles obviously, and they have different lifecycle however I am giving an example how the PS4 in 2018 was doing 250-300K per week and no one would believe that in 2 years will have these big drops in sales to 8M in 2020 and to 2M(still questionable) this year. Just like the PS4 death was probably the biggest and the worst death out of all consoles, till now this can happen with every other console too (if the manufacturer don't make the right steps). So just never say never, because everything is possible. Even the haters and no sayers in 2018 were saying a little better numbers for the PS4 ahead than they are now.
If Nintendo launch the successor in 2023 Switch will not pass 130M lifetime.