I’m with thisparachuteisanapsack
Yes it’s rude, but sometimes I’m just unexpectedly out of action and can’t face even looking at messages.
If this is possible then another message just saying “Hi there, everything ok? Would you still like to meet this weekend?” wont cause stress and will more likely get a truthful response if they are struggling. I’m apologetic and explain if I find I can’t manage something.
If they are just not answering yes it is rude, it happens, definitely follow up if the person is otherwise respectful to you. Again just a “Hi there, just checking in about this weekend, still on?”
If they’ve missed the first message, the second is reminder and ignoring two with no reason is a good moment for you to think ok fine, I’ll rise above it and eat all the cake myself!
I’ve had friends get very selfish and self involved, their world and schedule is the only one that matters. Kill it with kindness, helps you not feel dragged down! Just a “Haven’t heard from you, hope you are ok, anything I can do to help get in touch” works if you can’t teach them with a second attempt. Then eat the cake:)