For the sake of completeness (not endorsement), here is what a typical Victoria 2 DLC Unlocker installation process looks like:
Common outcomes after 10-20 hours of play:
Authorized retailers (Green Man Gaming, Fanatical, Gamesplanet) often sell the Victoria 2 Collection for $7-12. Avoid grey-market key resellers (G2A, Kinguin) as keys may be stolen or region-locked.
If a friend owns the complete edition, Steam Family Sharing allows you to borrow their library (including DLC) for free—legally. You just need a trustworthy friend.