I do not exercise.
(Caveat: I will refrain from taking any advice that would lead to me starting to significantly exercise until I have a diagnosis and a treatment plan of my apparent heart condition, which doesn't indicate it would be unsafe or otherwise a medically bad idea. I'd be really surprised if my doctor told me not to exercise, but in case she does I want to wait and make sure that my body is really lying to me when it says "don't do that, bad things will happen".)
Reasons (and existing known routes around each):
Sweat is horrible, and I overheat too easily. (Swimming gets around these; outdoor exercise in cold weather, interestingly, does not.)
Sunshine is horrible (and other environmental issues). (Anything indoors or at night gets around the sunshine thing. Other environmental issues are mostly limited to smelly gyms and excessively humid indoor pool facilities. Anything outdoors and at night and in nice weather gets around this.)
Many forms of it are financially costly (equipment, facility use). (Going for walks does not have this problem.)
It is boring. (When I tried jujitsu, it did not have this particular problem. Merely being able to listen to music does not solve this, although it could combine with another partial solution. If this problem is solved by simultaneously watching a movie, it has to be in a context where I can turn on subtitles, because I will not be able to reliably hear dialogue over any non-perfectly-silent form of exercise.)
Known route around all of these problems: happening to have free access to an outdoor pool which is open at night and a person who will go with me and chat while we both backstroke laps. This would be great but I don't happen to have access to a free outdoor pool that is open in the dark.
I do the Five Tibetans every morning, and they may meet these requirements.
They don't raise a sweat on me, except for the 5th. I can't say whether they will for you.
I do them indoors.
They are free.
They only take 10 minutes -- much less if you're not doing the full 21 reps of each exercise. How long does it take for you to be bored?
This isn't the only thing I do for fitness, but it does seem to have a significant effect for me. The other things I do probably don't meet your requirements: using a bicycle for transport whenever practical (sweat and...
An exercise:
Name something that you do not do but should/wish you did/are told you ought, or that you do less than is normally recommended. (For instance, "exercise" or "eat vegetables".)
Make an exhaustive list of your sufficient conditions for avoiding this thing. (If you suspect that your list may be non-exhaustive, mention that in your comment.)
Precommit that: If someone comes up with a way to do the thing which doesn't have any of your listed problems, you will at least try it. It counts if you come up with this response yourself upon making your list.
(Based on: Is That Your True Rejection?)
Edit to add: Kindly stick to the spirit of the exercise; if you have no advice in line with the exercise, this is not the place to offer it. Do not drift into confrontational or abusive demands that people adjust their restrictions to suit your cached suggestion, and do not offer unsolicited other-optimizing.
To alleviate crowding, Armok_GoB has created a second thread for this challenge.