How to install additionally Win 7 onto a system with Win10?

Assume I bought or got a desktop/notebook with a pre-installed Windows 10 system.
The hard disk is either MBR or GPT based and contains the typical partition scheme
with

Windows Recovery partition, Efi System partition, Microsoft reserved and Windows 10 main partition.

Now I want to shrink the windows main partition (with Win10 on it) and create a new partition on the free space for Windows 7.
Afterwards I want to install Windows 7 into this new partition.
(provided that the CPU architecture is Windows 7 compatible).

After all I want later to be able to boot the system, then press F8 and got the boot manager menu where I can select which WinOS to boot: Win 10 or Win7.

Is this possible?

Are there any important issues? Must the Win 7 partition e.g. after or before the Win10 partition?

Do I have to manually add the new Win 7 bootable partition to the BootManager or does it automatically recognize the new WinOS?

Does it matter if the hard disk is MBR or GPT formatted?

Peter

There is another way which may be better for you: Run a Windows 7 virtual machine inside of Windows 10. You may already have virtual machine software installed -- it will be called "Hyper V". This is something that Microsoft provides free of charge if your version of Windows 10 is eligible -- if you have Windows 10 Professional, Education, or Enterprise. Also, your system needs to be 64-bit. (If Hyper-V is not available, you can install some other virtual machine software.)

Set up a new virtual machine session, and install Windows 7 in the virtual machine.

If you do the above, then Windows 7 will be just a click away. You won't have to reboot in order to use it.

To do a Win 7 installation on a computer with Win 10 may not be easy as new hardware requires drivers that aren't on Win 7 installation disk. You must also have to disable secure boot on BIOS.
Create a Windows 7 USB flash installation with new drives for new MB's - Windows 7 Help Forums

"After all I want later to be able to boot the system, then press F8 and got the boot manager menu where I can select which WinOS to boot: Win 10 or Win7."
- Multi boot option is only possible if disk is UEFI - GPT. On a Legacy - MBR disk you can only have one boot loader (that can have dual OS option).

"Are there any important issues? Must the Win 7 partition e.g. after or before the Win10 partition?"
- It doesn't matter, but if you shrink the Win 10 partition, the space will be created on the right side.