Probably early next year. Nintendo's console cycle periods usually run for 5 years (the GC and Wii life cycle were 5 years and Wii U was 4 years) so I'm expecting their next console to be the switch successor, not an upgrade version of the switch.
Wii life cycle was 6 years.
OP: Switch XL should be announced early 2022 with a release within this fiscal year, probably March 2022. A proper Switch successor should follow 2025. If no Switch XL will be released, a Switch successor should launch 2024.
There's still a chance that a Switch XL will be released this year. Switch Lite was announced 10th July and released 20th September. Imo there's no real need for new Nintendo hardware this year. Nintendo, Sony and Microsoft still struggle to satisfy the demand of hardware and Nintendo is still selling out all competitors combined.