My smallest solos are probably Friday and a few Oniverse titles. I love Aerion and Nautilion the most, out of that series. I do enjoy Wingspan solo, been meaning to unbox the Oceania expansion, which I got because it apparently fixes the final round egg hoarding.
Coffee Roaster is fun and not big, also I'm a sucker for Cascadia - a couple of solo games back to back run to about 30-40 mins. Finally, been getting into Glass Road, which is pretty short.