If I can offer an alternate perspective..

By making such concrete plans you may be ceding too much "control" to someone who you don't yet know will have the same reliance on solid planning or respect for other's time as you do.

So, if that's the case, what can you do about it?

Plan differently.

Plan a one hour "date with yourself" that also works for you + a date.

Example: Make a plan to meet at a coffee shop or cheap bistro near a park... but bring a book/kindle/podcast/homework, or whatever you'd otherwise do on your own.

If they show, cool, you now have topics to discuss. If things are going well, continue over a walk in the park.

If they flake, cool, you've now got a solid hour to do something you enjoy, in a (hopefully) interesting place, and you've done it for cheap... Maybe take yourself on a walk in the park. :)

Hope that helps a bit.

5-1-0

Plan something 5-days in advance to do something.

Reach out 1-day ahead and ask if they are still up for doing it. It provides them with an out, and opens up your day tomorrow in the off chance that they have to cancel.

On the day of the planned activity, let them know you'll be heading out shortly to meet them at x place at y time.

For extra soft plans (i.e. do you want to get together and study later this evening?), still text before hand about an hour or so as it gives them a quick reminder, and allows you to alter plans.

Communication works both ways, and sometimes people need reminders. If they don't respond, just let them know you didn't hear from them and you're going to do something else. Don't freak out about it. People waffle on things all the time.

Oh boy. Another thing where I am happy to live in germany. No soft-planned things here. If there is a possible appointment (and we pretty much always do appointments to meet each other) we say yes, no, or don't know yet. Only yes classifies as planned. I know that in most other countries in the world this is not the case. I feel like germany is a very autism friendly country compared to most others when it comes to such ambiguous situations I read about online.

I don’t have answers, but you inspired me to contact someone just now because I was doing just that. Thanks.

I've honestly just stopped putting stock in people who are consistently unreliable with planning. Soft agreements stay soft and I'm always mentally prepared for a "oh I forgot, now it's too late sorry"

I will reach out in a lot of cases. If they consider me clingy or needy for asking for them to provide me with a reasonable expectation, then bullet dodged. I only want to date people for whom my need for clear communication and expectations is seen as a boon (because I'll provide the same in return) and not a burden.

Yep; anxiety bordering on dread.

But that's true whenever I'm supposed to reach out to anyone or meet up anywhere.
My brain just doesn't handle stuff like that in a reasonable way in general.

Gunna sneak in here. I have to say that friends are harder to come by now than ever before. But I also live in a place radically known for it's stanky people. So you know, it is what it is. But I still have some brilliant, wonderful and loving folks who remind me every day how wonderful human beings can be. So my suggestion to you here is realize that everyone is a flaky shit, we're all overstimulated and exhausted, people will show you how much they value you with their actions. I think there's something labeled for autistic waiting-mode but I don't remember what it is. The biggest thing I wanted to say is that the people I have loved endlessly in my life have been people with big hearts and a touch of (mayhapsby) neurodivergence or at least being strongly against the grain in nature. I mean I think some of my favorite people alive are bipolar people, and they get treated like absolute plagues of the world by most. So yeah, I think at the end of the day you've got to just find the people who work with you. But yet again, how you do that in this modern era? Hell if I know. If I hadn't laid so many mad roots all over the place I think I would be absolutely puck-ed right now. So it is what it is but godspeed and you've got this!