We require transfer switches, but they do not have to be automatic transfer switches.

In the United States, you are one small piece of sheet metal[1] away from any number of interesting power set ups on your side of the utility.

This means a combination of two circuit breakers is now your transfer switch. This is legal with all utilities and NEC compliant, etc.

If you are willing to sacrifice perfectly uninterrupted power, you can dramatically simplify your grid tie - and open up many other possibilities on your side of the physical interlock.

[1] https://www.daierswitches.com/products/sd-200vl-generator-in...