I general it’s pretty easy.
- disable secure boot in bios
- go in windows, shrink that partition
- boot into eos live USB, install/select on shrinked partition.
That’s it!
That being said, would be good to post more about your hardware, that’s the main problem. Are you using Nvidia?
And I guess with the new eos iso you will need to enable os prober to see windows at boot…
Edit: here how to do this, easy pisey!
https://discovery.endeavouros.com/grub-and-refind/grub-dual-booting/2021/07/