What is a good anti theft lock to use for apple Air M1 in a college dorm since there is no lock port?

As dorm “privacy” is by definition weak and preventing physical access is nearly impossible; additional “hardening” is in-order.

I’d additionally suggest the following hardening steps:

Enable 2-Factor Authentication if you’ve not already done so.

https://support.apple.com/en-au/HT204915

Set your screensaver to a short interval:

Require password after waking:

https://support.apple.com/en-au/guide/mac-help/mchlp2270/11.0/mac/11.0

Turn “on” your M1s File Vault if you’ve not already done so:

https://support.apple.com/en-au/HT204837#turnon

Lastly, set up an “Administrator” account on your M1 … w/ a DIFFERENT PASSWORD, while you normally login w/ a “Standard User” account.

There are none made by apple as far as I know, but there is a list of good third-party options here.

You should also turn on Find My and Activation Lock (Find My stays on all the time, Activation lock is only used when the Mac is lost or stolen).