Linux Lite and windows install

[stevef]

Is it possible to boot LL as usual but have a separate access to Windows just for running old Windows programs and nothing else?

Yes. I assume you are thinking of dual boot though you could investigate running Win10 as a virtual machine.

The usual approach to dual boot is to use Windows to shrink the partition it uses to make space and then install Linux Lite in this space.  You can then manipulate UEFI and grub so that one of the installed OS (LL in your case) boots on a normal start up, but the alternate OS can be booted if required by intercepting the boot manager to select the alternate OS.

As always, backup everything you need before.