Learn English – what is the personality trait for someone that can’t think fast, slow learner etc

Consider,

backward-looking

Concerned with the past rather than the present and future FOD

living-in-the-past

live in the past: Fig. to live while dwelling on past memories without participating in the present or planning for the future. You are just living in the past. Join us in the twenty-first century. McGraw-Hill Dictionary of American Idioms and Phrasal Verbs

past-ridden

ridden: adj. dominated, harassed, or obsessed by. Often used in combination: disease-ridden; grief-ridden. American Heritage® Dictionary

stick-in-the-mud

Someone who has old-fashioned ideas or who does not like trying new or exciting things. M-W

Uncomplaining

: accepting, doing, or dealing with something difficult or unpleasant without complaining