It'll happen. Nintendo is predicting 4m for the worst 13 weeks regarding shortages (Jan-Mar) - averaging around 315,000 per week. Even with that weekly average from April to September, Nintendo will not be far off from the 8.7m they managed last Q1/Q2, and demand will, of course, be much higher.
For the holiday quarter, shortages should be easing up this year, whereas last year the holidays were when stock began to have problems, so there's no reason to think that another 10m+ holiday quarter isn't in the cards for Switch in 2022.
I really don't see a scenario where the Switch does less than 22m this year, save for stock taking some unforeseen nosedive as the year goes on.
The only scenarios I can see pulling Switch below 20 million for the year are if the chip crunch worsens instead of improving, or if Nintendo decides to announce or release the successor this year, which could see Switch do a PS4 and be quickly sidelined in favour of pushing the new hardware due to limited production capacity.
There's zero chance Nintendo launches Switch's successor this year.