That is an interesting question. What would my lockdown camera be?
I think I would take a Fuji X100V. It is a very complete camera with even a built in ND filter. It is easy to carry. OVF, EVF, and flip screen. You can use it for snaps or more disciplined tripod photography. What I have learnt from my X Pro2 with a 23mm lens is changing aspect ratio can really make for variety in the appearance of your work: 3:2, 1:1, 16:9. Naturally, with digital, you can stitch panos as well. (And it would protect me from the inevitable one camera and two lenses...you guys understand how that goes.)
While I obviously enjoy the quality of larger formats, I really have not enjoyed the weight and bulk. Those are starting to become more of a hindrance to going out and shooting. I have come to appreciate high-quality compact systems. There is really no reason to leave them home and, when you are out, you are ready if inspiration hits you. Hard to do that when the large camera is safely at home in a bag.
Although, if I went big, just for fun I would like an Actus Cambo with a Sigma FP and a medium-format 35mm lens. That would be fun, but in reality, I probably would not get as much use out of it (see above).