All mains connected solar has an inverter. Hell, most wind is part or fully converted, to smooth out the raw waveform, and thus is inverter driven.

Where I'm from your "interlock switch" would be called "island mode". It can be a thing, but distribution network operators have a legal obligation to maintain supply (or else they face harsh financial penalties) and as such they are reluctant to allow even the possibility of unintentional backfeed to their network, especially when they need to work quickly to keep supplies up. Safely regulating every single household is just too burdensome, not without extensive modification that no one wants to pay for.