My 2020 MacBook Air fan is running constantly

If your MacBook Air fan is consistently running, it could be due to background processes or apps using system resources. Check Activity Monitor to identify any resource-intensive applications. Additionally, consider resetting the System Management Controller (SMC) to recalibrate fan behavior. If the issue persists, a visit to an Apple service provider might be advisable.

Perhaps your build model MacBook Air has no cooling fans at all.

Several years ago, they were to go fan-less. Therefore, fair reason

to not enclose those inside a case. The chassis being metallic, does

a fair job of radiating heat away from the all-in-one 'System on Chip'.

..If your build year is not an Intel based CPU, it'd be Apple Silicon..

https://duckduckgo.com/?t=ftsaq=which+macbook+air+model+years

+have+no+cooling+fan%3F&ia=web

You may decide to look into Activity Monitor application and see what

is there, running inside that version's macOS. Could be just some flaky

anti-virus or other mindless software which has no place at all in Mac?

Also you may try EtreCheck app, to see who's inside there goofing off?🙂