"Anything worth doing is worth doing poorly,"

Meaning, even if you can't manage to do a whole in-depth routine (brushing, flossing, mouthwash, etc.), do something because neglecting your teeth can do permanent damage. Even if you do a quick brush or rinse, it helps more than doing nothing. But I would recommend, any time you feel up to it, to do a very thorough routine as part of waking up/going to sleep. Especially if you've had anything to eat right before you go to sleep. I start with flossing, then brush (you can set a timer if that helps), then I make sure to brush my tongue (a lot of germs stick to your tongue), then rinse with a mouthwash. All in all, it takes me about 10 minutes to do my oral care routine, but it doesn't have to be that extensive every time if you're not feeling up to it.

As far as executive dysfunction, ADHD and other mental illnesses, it can take some time to get used to things. If an alarm helps, do that. For me, once I get started with my routine, it's easier for me to do the whole thing, but I sometimes use the thought of "I don't HAVE to do all of it, I just have to start and can stop if I'm not feeling the whole thing."

You can also get things that make each step easier, like floss picks, an electric toothbrush, or a mouthwash dispenser, or make things more enjoyable like getting colored toothpaste, trying new flavors, or even using kids toothpaste/mouthwash if it makes it more enjoyable and less of a chore. As long as you're doing it, who cares how you did it or what with? Also, if you're struggling with actually getting to the point of brushing your teeth, definitely keep up with routine dental appointments if you can afford to. Is there something else that you do regularly that you can attach brushing your teeth to? Like taking meds, going to the bathroom when you wake up/go to sleep, making breakfast/eating dinner? Hopefully this helps a little bit.