My prediction is as follow with a baseline of 77 mil sell-through as of end of 2020. Because of the semiconductor issues my list has faults but I commented accordingly:
2021: 25 mil (effective: 24.85 mil.)
2022: 24 mil. (this number is wrong but before Nintendo made any corrections I predicted 26.5 mil. in 2021, I just added those missing numbers to 2022, when in reality it will be even out over more than one year)
2023: 18.7 mil.
2024: 14.8 mil. (20% decline)
2025: 11.4 mil. (23% decline, Switch 2 comes out in March, however as decline was massive the year before, the decline stabalises despite Switch 2)
2026: 5.7 mil. (50% decline)
2027: 2.85 mil. (50% decline)
Rest of life: 1 mil.
Total: 180.45 mil.