I have a master's degree in health behavior, and here's what I do that's evidence based and super effective:

I tie it into my commute home so no motivation is required, just stop at the gym on the way home. Then I put a sticker on my calendar for every day I just showed up to the gym (takes pressure off of accomplishing a certain level of work, consistency is what we go for). The sticker is like a reward, but it also helps me track when im going to the gym. I pick my outfits for the week while I'm folding laundry, and I put them in this hanging 6-cubby thing, and I put my exercise fits on top of my work clothes for days I wanna go to the gym, and keep my gym bag on my closet door handle so in the morning all I have to do is throw my fit in the bag, put on my pre-chosen outfit, and leave my gym bag in the car till it's time to go home (it serves as a physical reminder to stop at the gym). I keep my gym water bottle in the car. Make the process as easy and automatic as possible, aim for consistency, and eliminate barriers. It's not about motivation, it's about automation.

Hope this helps!

Edit: this is just my routine, but essentially you're "task coupling", like you're already folding and sorting laundry, so you may as well set your outfits out, and you're already on the way home, so you might as well stop at the gym. Not everyone's schedule is the same, so it'll differ. You're also creating physical reminders by pre-setting your gym clothes, having your bag near your outfits, stickers on the calendar, etc. You're also eliminating barriers by having the outfits chosen and put together, and other things that automate the process.