You are contradicting yourself as you can see from the bolded part you claim that the house edge is fixed for all sites but the second bolded part, you claimed that it changes based on the number of deck
If you take a look at my post just above you , you can use those calculator on those sites to check that each sites have the rules that will determine the house edge for the BlackJack
Several rules that may changes the house edge of the BlackJack game :
#1 Number of deck used (obviously)
#2 Soft17 rules (dealer stands on 17 or more)
#3 Double after split
#4 Number of splits available
#5 Ability to split aces
#6 Ability to hit ace after split
#7 BlackJack pays 3:2 or 6:5 rules
Each site has a different rules , therefore the house edge for Blackjack games are different as well
yes, arallmuus is correct, different bj rules have different house edge,generally the more decks, the higher house edge, one deck bj house edge is minus, so the expect return for casino is minus, so we can rare see 1 deck bj nowadays, instead 1 deck, casinos offer 8 decks of cards, the house edge may be as high as 0.6%, but it's still very low compare to other games, if we have decent strategy, and good luck, we can beat the house.
Best I've been suggested yet is coinroyale.