In version 1.6.0 of Fuse in Debian GNU/Linux 12 (bookworm) aarch64 the address Start is always 0 when you choose Load Binary Data dialog. I think Fuse should remember what you chose last time for Start in a session, since you often load binary data to the same address. E.g. in order to LOAD a program in a ZX81 emulator for ZX Spectrum you have to load to the same address every time. It is good that length is filled in automatically and that Fuse remembers the last chosen file. .P and .p should preferably be Supported File types for binary files, so that you don't need to select All Files in the file open dialog.
The same about Start goes for the Save Binary Data dialog.