Skyrim adlevel cheat not working
Solution 1:
There is no player.addlevel in Skyrim which is why you are receiving the error.
Player.SetLevel [#]
Sets the player level. However, it does not grant the experience you would gain normally, it just modifies the level.
Alternatives are:
Player.AddPerk [perk ID] Adds the specified perk.
AdvSkill [[[[[Skill|skill]]|skill]]] [#]
Source: https://www.ign.com/wikis/the-elder-scrolls-5-skyrim/PC_Console_Command_Cheats