Other half has ADHD tendencies (also undiagnosed, but so obvious!). When he's absorbed in anything (phone, laptop etc.) he genuinely can't pull himself away. I can be having a conversation with him and he won't know it l, but it's not intentional. He's a wonderful dad and partner, and great with his job, but very forgetful with some things and struggles to remember things or where he's put items.
We developed several coping strategies when our baby was born, to help us both manage and reduce the workload of other life stuff, so we could focus on DD more:
I write a weekly schedule of things (house/baby chores) that needed to be done, day by day, along with timings (e.g. childminding 8am-6pm).
We have a shared family calendar online which sends reminders for events - everything goes in there.
We use Trello to manage life admin. It's free and you can create 'boards' for different things (house, garden, baby etc.). You can assign people to different things, set deadlines etc. It's great for getting things 'out of your head' and into an organised area, where it won't get forgotten.
A mini whiteboard in the kitchen with a weekly schedule on - we sit on a Sunday and check the week ahead, write appointments etc. on it and also meal plan. We go through our Trello boards to see if there's anything we can prioritise that week.
If other half is in a situation where he needs to focus on her (e.g. she's eating in her highchair) he doesn't have his phone, as can't guarantee he'll be watching her.
When he's focussed on her for long periods of play or care, or doing chores, he uses earbuds with an audiobook.
If I'm tidying or doing something with DD and I want him to engage or help, I ask.
When talking to him about important things, I check he's listening and get him to repeat it to me after. Still end up repeating things lots (e.g. putting nappy bag in the boot rather than next to her, do it doesn't injure her if there's an accident).
I regularly send him videos on socials of baby safety tips - he seems to absorb them a bit better that way. He is quite anxious about DD's wellbeing so that possibly helps with him remembering or being concerned with that stuff.
It's a lot to think of and you do sometimes end up feeling like you're nagging and having to mother or instruct another adult, but the organisation stuff takes about ten minutes a week once you're in the routine and it's worth it to make things work.
He would need to be open to doing these things though, my OH initiated a lot of this as he has always used to-do lists to cope.