I’m trying to game share with my brother save the world from my main account to a different...

Yes of course, I’m logged into the same xbox live account when I am the one playing, and I do do game sharing with digital games that i purchase with my brother, and he game shares with me. My save was syncing perfectly fine for a while i could continue
my world on the other xbox, and then continue from there again on the first xbox.

Are you both using the same console? From what I understand, game sharing needs 2 consoles as each needs to be set as the home console to game share....my guess would be, with only one console, you'd need something like Ultimate Game Pass to be able for other accounts to access the games you own.

At least, that's my understanding but I'm not an expert at consoles or game sharing etc

try to go on a different account and download it from that then go back on to your main account and game share it

I just tried. The game only shows up in my main account not. If I try another it doesn't show the "Install" button.

try to go on a different account and download it from that then go back on to your main account and game share it

I have 1 account but share my Xbox with my brother and I’m the one that bought it so in total there’s 2 accounts on the Xbox but we don’t go onto watch others accounts