Since I've got miserable arms too, I mostly rely on voice notes when I'm out and about and want to capture an idea that pops into my head.

Oh, and having completely random notes in your Zettelkasten is completely fine. In fact, it's great. Just make sure you don't forget to look for connections between ideas.

Here are some prompts I use to find connections between ideas:

Can you think of an analogy?

When does this apply?

What are the properties of this?

When does this not apply?

Can you think of an anecdote that illustrates this?

What’s an example of this?

Why is this important?

Why do you agree with this?

Why do you disagree with this?

What does this remind you of?

What is this a part of?

What is this similar to?

What is it better than?

What is it worse than?

Where did it come from?

What does this mean?

Have you experienced this yourself?

What is this different from?

Why is this different?

What is this really about?

What problem does this solve?

What problem does this cause?

How would you improve this?

How would you change this?

How would you explain this to Fabi?

When have you experienced this in your life?

That said, you need way more than just two notes for a ZK to become useful.

Think of a ZK as a personal Wikipedia of ideas. It would be pretty useless if it just contains two ideas. But if you had a personal Wikipedia with thousands of ideas all explained in your own words so that you can understand them easily and each of those ideas is connected to other ideas, you've got a super powerful writing support tool right there :)