Goal is kinda simple:
I want to install Ubuntu Budgie alongside encrypted Windows partition, and enable encryption on newly created Budgie installation (not just /home, but full partition).
The question is how to do it? 
PS.
I don’t want to erase current Windows installation.
Hi and welcome!
this question is also applicable to all of the ubuntu community - so I would also ask on askubuntu.com and ubuntuforums.org where the wider ubuntu audience can help.
For further generations here is the answer I was looking for:
Are you looking to have Windows & Ubuntu on the same drive or did you want to have them on separate drives? I currently have both Windows & Ubuntu on my computer as a dual boot with 2 different drives for the boot drives. The issue that I have experienced with running a dual boot of Windows & Linux is that no matter the order in which they would be installed, the Windows Boot Manager would take over in BIOS. By having the Windows Boot Manager take over in the BIOS, if I would go to do a fresh install of Windows, I then have no access to Linux. Are you looking to encrypt the Linux partition so that it would not be able to be accessed by Windows? What I’m actually going to be doing shortly on my computer is I will be doing a fresh install of Ubuntu Budgie 22.04 and then I will be wiping my Windows drive and turning it into a virtual machine on Linux, since there is very little that I need Windows for that I can use for Linux.
I think that’s only doable if you have a second disk. Then you can finish the job.