Got a M2 Max 16" a few months ago, and I think I should be able to easily last on it for six years. My plan when buying it was to just use it until they stop offering macOS upgrades and then buy whatever is current at that time. (I've been doing this with iPhones for a good while now; just recently switched over to Mac.) I am already setting aside some money every month for this purpose so it won't be a big lift to spend a few thousand on a new laptop in six years or so.
I might upgrade sooner if there is a compelling reason to do so... But I am not sure what that would be. The system performance is great and I don't see anything coming down the pipe that would give me trouble. I do gaming, but my backlog is so huge, I am fine waiting even for a few years to play a game if the performance demands are too great for my current system. I am a data packrat and I would like them to raise the SSD storage cap (and lower storage prices), but for now, moving "bulk" stuff to network storage works well enough. An OLED panel would be enticing but also I wouldn't want to be in the first group of people getting those; I'd want to make sure that things like burn-in aren't a problem before committing. Hearing rumors of OLED MacBook Pros coming in maybe 2026-ish, so 2029 sounds good for an upgrade.