The Anglo-Saxon nobility had some distinct titles that would be ideal for adding some extra flavour to the game, however the system was also different from that of contemporary France, with fewer titles of nobility. This makes it harder to effectively translate from real life to game, however I have some proposals.
Knights become thegns - these were the warrior class, some went on to become barons. I have no doubt someone will suggest housecarl instead, but the term was introduced when Cnut conquered England and even then it was sometimes used interchangeably. Thegns were also very important and CK3 knights seem to be more important than CK3 barons.
Baron (castle holding) becomes burh-reeve - reeves were government officials (the most notable one being the sheriff), and whilst burhs were NOT castles they were fortifications (often as part of a town protecting a royal mint). Without giving the Anglo-Saxons a unique holding or radically overhauling the system, this is the best fit for now.
Mayor (town holding) becomes port-reeve - again, another type of reeve, with port meaning market than a seaport.
Count (feudal) becomes ealdorman - the highest title of nobility, and in post-Danish conquest became earl. However in the early game when the kingdoms are duke-tier ealdorman fits perfectly, being in charge of shires or ealdormanries (ealdormanry being more appropriate term for the shires outside of Wessex).
County (republic) becomes shire-reeve, or sheriff - very common government official in charge of a shire
Duke (feudal) becomes earl - technically same rank as ealdorman, but post-Dane conquest Cnut divided the kingdom into great earldoms, so this is when the term becomes relevant. There were some minor earls and in-game these can continue to be called ealdormen.
Duchy (republic) becomes high-reeve - highest rank of reeve, equal weregild to an earl, quite a rare title but existed in Bamburgh (duchy of Northumbria in-game) for a time.
If possible, levies to become general-fyrd and men-at-arms to become select-fyrd (fyrd being the Anglo-Saxon army and select-fyrd being the more professional soldiers).
Commander could be heretoga, an Old English word for an army commander.
Knights become thegns - these were the warrior class, some went on to become barons. I have no doubt someone will suggest housecarl instead, but the term was introduced when Cnut conquered England and even then it was sometimes used interchangeably. Thegns were also very important and CK3 knights seem to be more important than CK3 barons.
Baron (castle holding) becomes burh-reeve - reeves were government officials (the most notable one being the sheriff), and whilst burhs were NOT castles they were fortifications (often as part of a town protecting a royal mint). Without giving the Anglo-Saxons a unique holding or radically overhauling the system, this is the best fit for now.
Mayor (town holding) becomes port-reeve - again, another type of reeve, with port meaning market than a seaport.
Count (feudal) becomes ealdorman - the highest title of nobility, and in post-Danish conquest became earl. However in the early game when the kingdoms are duke-tier ealdorman fits perfectly, being in charge of shires or ealdormanries (ealdormanry being more appropriate term for the shires outside of Wessex).
County (republic) becomes shire-reeve, or sheriff - very common government official in charge of a shire
Duke (feudal) becomes earl - technically same rank as ealdorman, but post-Dane conquest Cnut divided the kingdom into great earldoms, so this is when the term becomes relevant. There were some minor earls and in-game these can continue to be called ealdormen.
Duchy (republic) becomes high-reeve - highest rank of reeve, equal weregild to an earl, quite a rare title but existed in Bamburgh (duchy of Northumbria in-game) for a time.
If possible, levies to become general-fyrd and men-at-arms to become select-fyrd (fyrd being the Anglo-Saxon army and select-fyrd being the more professional soldiers).
Commander could be heretoga, an Old English word for an army commander.