This is a big problem that is hard to solve.
I actually like exercise. But I have some chronic illness that causes fatigue and muscle pain - even every day activities feel like hard exercise in that they cause pain like muscle burn. In order to try and do regular exercise, I have gone through so many exercise philosophies and plans and methods trying to identify my "problem" and solve it.
But a couple of months ago my baseline improved a lot for some reason and now I am tired but not fatigued, and it doesn't hurt to move. And it is easy to exercise. I barely need to put effort in because it is not HARD and PAINFUL and it doesn't make me feel WORSE. I just make an exercise plan and do it. Or don't make a plan and still do it. The difference is like night and day.
Exercising is very difficult when your body is not on your side. Its so so much harder than what the normal motivational advice is trying to address. So don't feel bad for struggling or for feeling the advice doesn't work for you. I didn't realise my problem wasn't "lack of motivation" until my body started cooperating - I have the same motivation but now its easy. The problem wasn't me.
You have to really want to do it. I know people say you have to find something you enjoy, but if it sucks really badly then you really really need to find the thing that sucks the least and do that no matter what it is.
You can swim, walk, dance in your living room, do yoga, do exercise lying down, do chair yoga, do isometric exercises (holds rather than moving), you can pick one single exercise you like, you can exercise for 5 minutes, you can do literally anything and you should - when exercise sucks you have to throw all preconceptions and expectations about what exercise is and what you should do out the window because your goal is to do anything.
What I did when exercise was too tiring and painful, but what works for you would be different.
For some reason I like basic bridges. I will do bridges but not other body weight exercises. But JUST doing bridges is still exercise and actually quite a good one because it helps your core. BUT that's not why we choose exercises - we choose what we CAN do, not what someone else says is "best".
A ten minute yoga video was manageable and even when it seemed like too much, I knew it helped with my headaches which would motivate me.
I like walking and thinking about stuff. I find it easier to think when walking, and if I'm thinking stuff hurts less.
One hour martial arts class - I started with 30 min and its a gentle class. This class left me exhausted the next day but it meant a lot to me to be able to do it at all so I kept going. I had to give up martial arts 20 years ago due to illness and the grief was massive. I was willing to sacrifice a lot to go to this class.
What I hope to keep doing when my baseline decreases again.
Hybrid calisthenics (website and he has a tumblr). These exercises are difficulty graded and don't need equipment. I hope that when I feel worse again I can step the difficulty back down but keep them up. I do the schedule where you do just one exercise a day, to keep it manageble.
(easy) Isometric exercises - these are where you hold a weight or position rather than move. I just discovered them and I think they would be easier for me to manage in my weaker and worse times.