From GameWatcher: “Bayek from Assassin’s Creed Origins is now available in Assassin’s Creed Odyssey! Here’s how to unlock Assassin’s Creed Odyssey Bayek, but what do you do if lieutenent Bayek is not unlocking?
We’ll show you all the steps to unlock Bayek, but be warned, there may be bugs ahead…”
Source: N4G PC Assassin's Creed Odyssey Bayek: How to Unlock Bayek from Origins