Instead of using dual boot by dividing partitions, why don't you first try using a virtual machine such as a virtual box or others to test specific operating systems, including PGP Signature on different OS?
I use MacOS as the primary OS. I run other OS using a virtual machine for testing PGP Signature or another application.
Well, I didn't realize I am this much bad at setting up OS. I thought it wouldn't be that hard to set up OS in dual boot as I already shrank enough space for the Debian 12. I always get a suggestion from time to time to switch to Linux. So, I wanted to migrate there but I wanted to keep the Windows OS as well. A virtual machine could have been a good option, but I don't know why I didn't try a virtual machine first.
I had some weird experience setting up the OS. I have two SSDs installed and I installed the Debian 12 on my 240 GB storage. For some reason, if I unplug my other SSD which is 500 GB, the OS does not boot. This is weird. So, I removed that SSD again and installed Windows again. Now I am setting up the Debian 12 again. I hope everything will be fine after this attempt.