For me, I find it sometimes helps to slow myself down and be mindful. For example, I frequently forget if I’ve locked my door or not, or if I’ve packed items such as my wallet or keys before work. I will deliberately slow myself down when I do these things, and even say to myself, “I’m locking the door right now. The door is locked.” Rather than getting caught up in the thousand thoughts in my head at the time, I focus on tasks.
For appointments, I enter them immediately. I usually do this when I’m at a doctor’s office or at work. If possible, I also get a physical card or appointment reminder as I can put them in my wallet and review them periodically.
I spend time setting things up in advance. The night before I will lay out my clothes, my wallet and keys, and even set the coffee maker to autostart. If you have one that stays on, it might be worthwhile to spend the money to get one with auto shutoff. That’s one less thing to worry about. I also make a habit of putting certain items in the same place all the time. It doesn’t always work, but for the most part it does.
In general, there are still days I’m super forgetful. Even with medication and therapy. It’s about progress not perfection. I may never be great at keeping it all together, but I have learned ways to get better over time. There are apps and things that can help, and other tools such as bullet journals or coaching. Whatever works for you. Good luck!