Can I uninstall Monterey 12.1 from my Macbook Air?

If you installed it from a previous OS, you can erase the drive and install the older OS or restore from the backup you made prior to installing Monterey.

If it came with Monterey installed, then most likely not.

There is no "uninstalling."

You can download the OS you want to run and create a bootable USB installer from that download.

Then, you boot from that, erase the drive, and install the old OS. You can then Migrate from your backup.

If you can do one of these procedures ti get back your Mac to a older macOS then do it but if you don’t know how to do a downgrade I highly suggest you don’t do it

read

https://support.apple.com/en-us/HT204904

As per the Licence of Use from Apple and mentioned by both previous posting - If the Computer came pre-installed with Monterey as New - Apple will disallow Downgrading to any version older than the Original Version it came installed with.

To make things more clear - the Oldest version of macOS this computer can downgrade to it Monterey - period.

Further, to be accurate and correct

Big Sur was released in November 2020

Monterey was Released Oct 25, 2021

Is is suggest working through the issues presented on the present version of macOS and not waste you time attempting and struggling to try and fail to install Big Sur.

Note that you can't install an macOS version older than the version that initially came with the Mac.

I'm download the macOS Big Sur again, cause this new one sucks!!!!!!!