First, it’s not only you: making plans that accommodate everyone’s schedules and budgets can be tricky, especially if a lot of people are involved, so you might not be doing anything wrong. You can try letting them know what you want to do earlier in advance so that they know not to make plans for the day. People are more likely to respond to concrete dates, times, and locations instead of vague ones.
Also not all of your friends are going to share your hobbies and interests and that’s ok. Try inviting just the ones you know for sure enjoy the things you do, or joining clubs or activity groups for those things to potentially meet new people to do them with. The time with your other friends can be spent on things you know they want to participate in and can afford.
Appreciate the honesty about the AI disclaimer.
Language learning is one thing that can be done when you only have your phone on you but want to be productive. Browsing Wikipedia can also lead you down some interesting rabbit holes where you end up learning something new. I’ll also use downtime to clean up my files and photos.