Hello, First of all, the ground bearing coefficient and bearing capacity values seem wrong in your project. You can review the knowledge base link below for the relative floor drift problem and possible solutions.
-We also recommend that cassette flooring systems be solved with the semi-rigid diaphragm method. - If there is no wall on the beams in the attic, you can remove their load. -The lower arm of the stairs on the ground floor is not supported on the foundation due to the level difference. You can define a basement curtain at a suitable height for the lower arm of the stairs and associate the edge of the stairs with this curtain. -While determining the support conditions for the solution together with the structure, it should be determined that the edge of the stair is only attached to the element that is supported, other carrier elements and other edges should be left blank. Good work