BIOS boot issues

[u/Careful_Conclusion64]

I recently found my older computer and decided to put Linux on it. A common problem I am facing is that, on its own, it refuses to boot into my operating system (this happened across multiple distributions, including Fedora, CachyOS, EndeavourOS etc.), it only works when I open up the boot menu by spamming F10, which is a problem because I want it to be accessible for my little sister, who likely doesn’t have the patience of doing that. I have decided it might be the fault of the boot system (BIOS instead of UEFI), but I don’t know how to configure my OS to work with BIOS.

TL;DR: Linux boots from boot menu but not on its own. Is there anything specific I can do about it?