How to fix MacBook Air reboot loop ?

Possibly - does the Area where the Battery is housed appear to Bulging ? That could be the cause as can Not Enough Empty Space on the Internal Drive.

If the Internal Drives does not have Enough Empty Space to even allow the computer to load the Minimal amount of the the Operating System which Safe Mode would have done - then >>

Transfer files between two Mac computers using target disk mode would be suggested before Find an Apple Authorized Service Provider

Try shutting down by any means including the Power Button.

Connect to charger.

Disconnect and external Drives.

Power Button and Immediately Hold the SHIFT key and only release after the Apple Logo is presented.

This is Safe Mode and dos a repair disk, clears cache files and Only Loads Apple Software, extensions and fonts.

This may allow the computer to boot up completely.

Do it ?

Can you boot into the Internet Recovery Mode (Command + Option + R) or Apple Diagnostics? If you still have the same issue with these modes, then you may need to "Revive" or more likely "Restore" the T2 firmware (Intel) or M1 firmware (the latter will destroy all data on the laptop).

Revive or restore an Intel-based Mac using Apple Configurator 2 - Apple Support

Revive or restore a Mac with Apple silicon using Apple Configurator 2 - Apple Support

Keep in mind the 2018+ laptops with the T2 security chip and M1 CPUs are almost like iPads now where boot loops are common and DFU Restores are necessary.

You should always have frequent and regular backups of your computer and any external media which contains important and unique data. FYI, it is impossible to recover accidentally deleted data from an SSD after the Trash has been emptied plus an SSD can fail at any time without any warning signs. In addition 2018+ Macs utilities a T2 security chip which hardware encrypts all data on the integrated SSD making data recovery extremely difficult to impossible if the Logic Board is not fully functional. There may be times when the T2 security chip becomes corrupt and requires it to be "restored" which destroys the hardware encryption keys which mean the old data is impossible to access because it can no longer be decrypted. Backups are way more important today than ever before.