when i use /locate commands and it gives me coordinates and i teleport there and nothings there, neither ground nor sky, fabric 1.21 mod

I was having a same issue, and took a while to figure what was wrong. It's the same Mojang/Microsoft bullshit as per usual:

Extract the pack, and on your pack folder you have \data\imst\structures. Change it to \data\imst\structure without the "s". Repack it, and use it. It's all good now.

It's my fault for forgetting path changes. Will fixed this month.