I have a MacBook Air (13-inch, Early 2014), do you suggest me to upgrade to OS Big Sur or not?

Upgrading to Big Sur is purely subjective. Before considering the leap to macOS 11 make sure to read this article from Apple noting computer compatible, Empty Space Requirements for successful installation. Also, note the leap to Big Sur - it and Catalina DO NOT support any 32 bit applications / extensions at all.

Due prudence is required before moving forwards. Have a Time Machine Backup Before upgrading and I always suggest have two TESTED Clones each to separate external drives - insurance in case Big Sur goes sideways or is not to your liking.

If you are coming from macOS Sierra (10.12), then the guideline is that you will need 45 GB of available storage, not shown by the menu : About This Mac : Storage panel, but rather a Get Info on your startup drive icon, and reviewing Available there.

I have a 4GB/128GB 2014 MacBook Air that was upgraded from Mojave to Big Sur 11.1. Works as expected with 4GB of RAM, and does not crash, and no other negative issues other than rapid battery decline — which should not be surprising for a 6 year old Mac.

Big Sur requires 35.5GBs of free space to install. Older 32bit apps will not run. That being said, I installed it on a 2013 MacBook Air without a problem.

You're welcome.