OK it is very clear now that there are no objections to a purchase of a M1 MBA for you!
This is good news

but leaves you to make your own decision ;-)
Air vs. Pro does IMO not matter in your case. The MBA can easily do anything you want. (But also the MBP can, or is there any specific reason for your wish for "extra power"?) "Pro" in the Apple world does not mean that the machines are more solid in general but have additional features and are better suited for heavy workloads as video editing, rendering, that sort of stuff. For example, your MBP has 4 ports to plug things into. The MBA has two.
How long Apple Macbooks last is a tricky question. The hardware as such is good for 7 to 10 years (there are always exceptions but your device has worked well for 3-4 years so why not some years longer). With newer software, computers tend to slow down but Office should not be a problem. I also think your MBP should receive macOS support until 2027 so that a 10-year-lifespan for your computer is reasonable.
It seems to me that it could be a matter of taste? You could easily keep your device, the specs are good. But maybe you want a new one? No touch bar, maybe you also don't like the keyboard at your MBP (?), and at the moment, you still get something when trading it in.
So, it boils down to "do what you want "