Google provides support for a minimum of three years, from what I can see.
None of the other big name Android phone makers issue long-term updates as far as I know, as they all customise each release and it's too expensive to do for anything but new phones.
For reference, the iphone 6S from 2015 is still supported by Apple updates - six years.
I could eg. get a secondhand iphone 8 64GB with a two year warranty from a national UK electronics dealer for half the cost of a new google pixel 5.
I often buy high-end secondhand rather than new lower grade, as the high quality stuff tends to be better performance and longer life.