A useful proposal idea is a scene you can actually stand in. Lists that start with skydiving are lists of spectators. If the person you are asking does not like an audience, the plan should get smaller, not louder.
Start from a place you already use
Pick somewhere that does not need a permit: the bench after the library closes, the kitchen after a shift, the stop where one of you always gets off one stop early. Write the place down in one line. If the line needs a famous landmark to sound romantic, it is not your place yet.
Add one memory that is not on a camera roll
The memory is the proof. A missed train, a bad umbrella, the last sandwich. It should be something a template cannot guess. Leave it out and the story is only a question in a room. Put it in and the chapter has to use it.
Decide the last line before you decide the production
Cards run out of room. A proposal comic has a last panel, which is a better place for the sentence than the back of a napkin you will lose. Write that sentence first. Then name the two people the way they should look in the drawings.
The comic is the printable version of that plan. You still do the asking. The pages are what is left the next morning, as a PDF or a stack of images, not as a video of strangers clapping.
What to skip
Skip a flash mob, a rented screen, and any idea whose main feature is that other people will film it. If you want more date-shaped gifts for later years, the anniversary list by year is the next page. If the story you actually want is the day you met, start at how we met instead of jumping straight to the question.