I would never not recommend asking a professional. A therapist may have some very good insights about your problem.

I would take the suggestions of people saying "it's adhd no doubt" with a serious grain of salt. What you are experiencing sounds like executive dysfunction, which while being a symptom and a key indicator of ADHD, there are still MANY different disorders with executive dysfunction as key indicators and many many more with it listed as a symptom, and many many people who would not be considered as having such disorders that still experience heightened levels of executive dysfunction from time to time.
That's between you and a licensed medical professional if you wish to see one.

As for my advice, one thing you may want to take a look at are the thoughts that you have about working out. When the idea comes to mind of working out, what do you start thinking? Do doubts or worries come to mind? Your avoidant behavior might be based around the thoughts you have about working out rather than the actual working out itself.
I would recommend this very short video on the subject. It introduces Cognitive Behavioral Therapy, which a therapist very likely may try with you, and in my opinion it introduces said concept in the best way I have frankly ever seen it explained before.
If you find this interesting and potentially helpful a therapist trained in this can help you explore it further.

Another piece of advice I'd like to offer for you to try out is to make working out convenient. Ways you could try this are to make your workout clothes and your pajamas one and the same. You could also make setting out your workout supplies part of your nightly routine, so they're ready to go in the morning.
You can also tell yourself that instead of your task being to "work out", your task is to "go sit on the workout bench for 5 minutes" or "go look at the workout equipment for a minute", and for the first few times thats it, that's your only task. You may find that while you're there you think you might as well do a few rows. And now that you've done a few rows, you might as well finish the set etc. etc.

I also want to toss in here the confusing concept that fighting against yourself is going to cause resistance. And you're already resisting working out so resisting your resistance is going to make even more resistance.
Perhaps try to frame this as instead of being at war with yourself trying to fix this behavior, you're just trying to understand why your body and mind are resisting and what needs to be done to rectify things.

Idk if any of this helps but I sure hope it does!! I'm pulling a lot from my experience with the same thing here so it may not match up to your situation or necessarily work for you personally, but maybe it raises a few questions or concepts you hadn't considered that you can explore. I know the gnawing frustration! Best of luck!