Repeat a mantra in your head. The mantra could be anything really. You do not need imagery to meditate. Another trick is to look at your hand and try to feel/sense the inside of your hand, focus on that.
I am on the other end of the phantasia spectrum; I have hyperphantasia. This causes problems with meditation because my ADHD gives me intrusive imagery.
The key with meditation is to just keep trying. Mediation is an incredibly useful tool but it is something you have to constantly practice. It is harder for people with ADHD to accomplish consistently but it is entirely possible to learn to do it well. If you practice enough you may learn how to live most of your life while meditating.
Learning how to meditate was the turning point to gaining control of my life and start on the road to a functional life. I am not saying medication (I’m on Vyvanse) and therapy (once a week for me) aren’t equally important or weren’t major contributors to better understanding and living with my condition but learning how to meditate and doing it consistently was when things started to click for me.
I’m with you. I meditate and I have aphantasia. I focus on my breath mostly, but as someone with adhd, my brain goes everywhere. The key is to not scold your brain for losing focus, but instead once you realize, note that you lost focus, and then gently bring your attention back to the breath. Meditation doesn’t have to have an end goal or a focus point or imagery or anything, really. I just like to take note of how my body is feeling, what my mind is thinking, emotions that come up, etc.
Find something visual to focus on. Focusing on breathing is another thing.
But, for me, it’s mostly just telling my brain no every time it tries to drift.
