I try to portray Agnarr, the adult at least, as someone who struggles with letting his emotions show, who dislikes conflict. who is fighting an inner one with himself. He struggles to truly be himself after years of being what other people needed of him, because of the traumas of war he saw upon the visit to Northuldra as a child as well having what little innocence he had left at that point upended by taking the crown at such a young age (14 is the youngest I portray him) because there was no regent/steward of the kingdom at the time of Runeard's death. A post Frozen/Frozen 2 Agnarr would not want the crown back, being mentally unable to take the pressure of having the crown upon his head and adjust to every new thing around him. It would take him time to adjust to everything, but he would be marginally okay by the end of Frozen (the second movie upends that stability hard).
The teen, however, is young enough that with patience and emotional support, he'll get over that trauma. Not entirely, but enough to where taking the crown isn't so terrifying. But, if we're talking before that, it's a bit of a.. Rapunzel and Mother Gothel situation (not rehashing it, just watch Tangled if you don't know what I mean) is the best I can put it. In fact, Agnarr goes to Lieutenant Matthias for things like emotional support. Even considering him as his real father and Halima Blodget as his mother because of the love and care they have shown him since he met them.