Sometimes 'Jeg orker ikke' means 'I don't have the energy.' It can mean a lot of things.
If you say: 'Jeg orker å løfte 50 kilo.' you mean to say that you can do it, you have the strength to do it. If you say: 'Jeg orker ikke å spise mer.' you mean to say that you cannot eat anymore. To have the energy to do something is 'å orke å gjøre noe'. Children say 'Jeg orker ikke' to everyhting they are asked to do.
Mother: 'Gjør lekser.' (Do your homework.) Child: 'Jeg orker ikke.'
I agree. For me the sentence 'jeg orker ikke' includes will and motivation. 'Jeg orker ikke' means all these things. For instance 'Jeg orker ikke å se den filmen en gang til.' (I can't stand to see that movie again.' This sentence is not about having the energy to do it.
Orker ikke is something like cba in english. https://www.urbandictionary.com/define.php?term=cba
There is some helpful information here: https://forum.duolingo.com/comment/16850825/The-word-Orker