Man, it has been a longtime since I did it, but I'll try and remember what I did.

How did you allocate the partition for Linux? Did you use Disk Management from Windows or did you allocate the partition as part of the installation process?

I think I installed windows first and Linux second, the other way around usually fucks with the bootloader, and then fixing it manually is a bit of a pain.

For allocating a partition, I had already freed space from windows to use for linux, before installing it

How do you share data between the two partitions? Do you create a third partition that both OS partitions have access to? Do you use external drives/flash drives? Or do you just have no need to share data between the two drives?

All I remember is you can access Windows partitions from linux as long as you disable secure boot. I think you can access the Linux partitions from Windows too, but I haven't booted Windows in a long time tbh, allocating a partition for both OSs is also a valid choice

Edit: when I said "allocating a partition for both OSs is also a valid choice", I meant as long as it's just a data partition obviously