When Assassin's Creed Valhalla first launched, I was happy to see that it did not include XP boosts among things players could buy with real money. However, a recent update to Valhalla's in-game store has changed that, and players are now able to purchase a multiplier to the XP they earn.
The change adds a "Utility" item to the storefront that costs 1000 Helix credits (the equivalent of $10), and adds a permanent 50-percent boost to the experience players gain across all of their save files. The same bonus can also be bought as part of a 1500 Helix credit ($15) combo that grants a 50-percent boost to both XP and money.
More: https://www.gameinformer.com/2020/12/16/assassins-creed-valhalla-sells-xp-boosts-now