for how long my phone will receive updates or on average how long a phone stops being maintained once it starts being maintained.
Until the maintainer decided not to maintain the device anymore. Could be tomorrow or in two years. It is impossible to say. Devices are maintained by developers for free in their free time.
how long my device has been supported, whether recently or around 2021-2022
around 2023-01-07. This info can be obtained from the official developer thread on XDA-developers