I feel like there’s a pretty straightforward answer to this. Rather than straight asking the question, you can ask for whether they have a moment to chat about

I feel like there’s a pretty straightforward answer to this. Rather than straight asking the question, you can ask for whether they have a moment to chat about _____. If you send that, now I know you’re asking for a synchronous conversation, and I can just say yes or no or “how about later?”