Your 2014 MB Air can run Big Sur quite nicely (MB Air 2013 is the minimum), but the threshold for Monterey for the Airs is Early 2015. Each release of macOS rises the level of hardware required to run it so on the one hand Monterey was described by some as more maintenance than evolution on the other hand it demanded more than some of the older hardware with Big Sur could deliver. Just about every iteration of macOS leaves some older hardware behind and embraces a new range of Macs.
As to upgrading to Big Sur - what are you doing with the Air after you upgrade to a new Mac? If selling it you will make it more attractive if it has the last system on it which it can support. Thinking longer term, if you give it away it will have the maximum capacity to your benefactor, if you keep it you can use it as a supplementary Mac for some years to come. In the interim you will benefit from the developments and improvements it has compared with Catalina. We have a number of semi-retired MacBook Pros which were replaced with new Macs some years ago. I use one or two of them occasionally and they can't go beyond macOS 10.13 High Sierra, but I upgraded them to that point to make them useful rather than languish on El Capitan or Sierra - on which Safari started to struggle with browsing, for one example of the problems of being out of date.
I've upgraded quite a few of our Macs to Big Sur and Monterey and had a good experience. My 2015 iMac is the oldest of these and it too performed very nicely with Big Sur and subsequently Monterey.
Others on this forum might suggest not to bother and that's a valid choice too. It just depends on what you want to do and find comfortable.
