Is using MacBook Air 2019 model without a keyboard protection safe?

If you need a keyboard protector because of the infamous Butterfly keyboard switch, a physical key protector may help prevent dust, but it could still very likely break. If you mean the physical protector, it might help but it also might not. However, in terms of a warranty, Apple will replace the keyboard for free (https://support.apple.com/keyboard-servi...). Hope this helps!