I dont think you should memroize too much but memorize what you use frequently and also maybe something you think is useful.
code completion/code hinting/code assist/param info/quick info in IDEs help you anyway.
Plus official docs. You may even learn a new thing or two.
And memorizing general algorithms and data structures is a must if you plan on coding professionalluly.
in conclusion, memorize only what you use frequently and what could be useful as tools are here to help!
And ds and algos is a must for professionals