Yeah, the official rules are such a party pooper. Only using black card when there's no other moviment possible are dumb, a lot of times (like when the next person has Uno) using it is the optimal and most funny play, even when you have more cards.
These online versions should have custom rulesets, because everytime I played were different rules.
All of them usually let you use special cards on top of +2 and +4, like the skip skipped your turn and made the next person buy the cards, and reverse made the previous person buy the cards (unless they also had special cards, so the combo would continue), but sometimes there were even more rules.
But one of the uncommon ones that I liked was this one:
If someone used a card that you had a identical one (same color and same number), you could play the card outside your turn, like skipping the line in a market or whatever, and then the game would go on with the player next from you. It had to be done quickly, before the "rightful" player to the turn to make their play, making the game more dynamic.