I've heard a lot of people stop meetings mid-conversation and announce "We're getting into the weeds" or "I don't want to get into the weeds".
It lets people know the topic is going off the original train, and is being hijacked to a less relevant course. Just announce it in a non-accusatory way, and ideally people will gravitate back to the point.
If someone pushes for something more off-topic but still mildly relevant, they're usually given command of collecting more details later, either at the end of the meeting or through Slack/email/etc. It's just important to stress the importance of tackling the core issues before getting into more cosmetic issues.