you seem to be requiring these characters to be in a constant state of objectification to receive the label

I'm not. It's about context. To treat objectification as some binary completely misses the point of objectification in the first place. As a facet of social philosophy, the idea has merit due to its context within culture and within the context of the media itself. Even if I agreed that a single sexual scene is objectifying (I don't) it would merely be in a semantic sense when (in the example of Thor) throughout the entire movie he is a multifaceted character who is clearly treated with respect by the creators.

Agency and subjectivity, in concerns to objectification, are so important because they're the whole point. When we assume the incredibly reductive definition of objectification as merely being acknowledged or treated as a sexual being we rob others of their ability to choose to embrace their sexuality. Thereby that definition of objectification is in itself objectifying.

Are you objectifying your partner by checking them out when they're unclothed? Are you objectifying your partner by having sex with them? Most likely not. How do I know? Because, presumably, your partner is exercising enthusiastic consent - they are exercising their subjectivity and agency within context of a healthy and respectful relationship.

To suggest a single scene fits a semantic definition of objectification ‐ as someone who had to study this stuff in university - completely misses the point of why objectification matters

Edit: you also seem to be relying on your past experience with this term for your understanding of it. I would advise against that. Many many many groups of people completely miss the point or misrepresent objectification