Is it possible setup this key type encryption in my computer?

Basically I need to setup a type of disk encryption security where my pendrive works as a sort of physical "key" to open my computer to boot. For only my main host os not tails specifically.

No, there is no such thing readily available. Even if it were to exist, what would be the point? The data in your main host is still not encrypted and accessible to third-parties that may eventually seize your computer.

You could create an encrypted partition in your main host and move the relevant data to there. What do you think of this approach?

Yes, the arch linux wiki tells you exactly how to.

!clearnet warning!

https://wiki.archlinux.org/title/Dm-crypt/Encrypting_an_entire_system#Using_a_USB_drive_to_unlock_/boot

Story of my life, lol