I didn't realise this with Gigantamaxes until I put my freshly caught Gigantamax Pikachu (Mr PEEEEbody) into Home, but I don't like how Pokemon Home doesn't show some of a Pokemon's alternate forms unless you put one in that's either in that form or capable of it. It does with some forms like gender differences and Mega Evolutions (I'm now in the fourth stage of grief for Megas in the main series), but not others like Gigantamax. I checked with Gengar as an example, it shows the regular Gengar and Mega Gengar, but not Gigantamax Gengar because I failed to catch one in the last Max Raid event it was in. I suppose it gives you more of an incentive to catch the Gigantamaxes in raids, I just think it's a bit annoying for the amount of extra work you need to put in if you're a Pokedex completionist. The only Gigantamaxes I have registered in Home at this point are Charizard, Pikachu, Machamp, Snorlax, Copperajah and Duraludon.
It's not just Gigantamaxes either, I remember the tedious task of putting a Rotom into Home, taking it out again, changing its form, putting it back in, and repeating until all six of its forms were registered (I thought it would be a better option than catching six different Rotoms). But with Alcremie, you only need to put in one that's, for example, Ruby Swirl with the pink heart sweets on its head, and it'll show that form with all seven different sweets. I suppose with Rotom the form change is a lot more substantial than it is with Alcremie, because Rotom's forms are all very different and Alcremie's are purely cosmetic, I just think it's a funny little detail.