The issue lies with the fact that is is not a conscious decision. It just... happens.

I tried this a while ago, unfortunately I would go off into something else in my head again and completely lose track of the answer I had at the ready.

So what I started doing to avoid that (but still hit points 1 & 2) is ask what I thought was the question back at them (in short form).

That seems to work well for me, maybe it will for others.

You can also wait for them to repeat themselves and will often find that their idea of 'repeating' is to say something substantially, meaningfully different.

Then you just ask them to basically pick a lane, settle on one actual thing they are trying to ask, and they will often get frustrsted by the idea of having to form and settle on a single, actually coherent thought, and abandon the attempt.

Or, get very angry.

In either scenario, if either of those happen, its now clear you are dealing with either a dumbass or an emotionally unstable / heightened emotional state person, which is useful information to have for formulating your actual response.

after they repeat the question you already have an answer ready to go

Or I already forgotten instead.

thats a lot of fancy words to say "i can have a conversation"