I want to put a receptacle in my soffit for holiday lights, and I want to use some kind of Z-Wave controller so they can be controlled with Home Assistant.

I haven't been able to find a GFCI Z-Wave receptacle, but I have found a Z-Wave relay. It's designed to control light switches, but I would imagine it could just as easily be used with a receptacle.

Since it would be outside, I'd probably coat it in epoxy in case water intrudes into the box.

Is there anything wrong with wiring a relay into a receptacle?

I'm not familiar with your futuristic "Z-Wave" tech,
but I thought GFCIs receptacles now have to be manually
reset if they don't sense voltage on the line side.

That would suck if installed up in the soffit.

Maybe a relay on a standard receptacle on the load
side of the GFCI outlet?

Use a regular receptacle in soffit, mount GFCI in attic that you can reach. Power for that through a Kasa or Z-wave switch. Easy to do.

Put a gfci breaker in the panel then it doesn't matter what kind of outlet you use?