I've tried leaving 15 minute buffers in between meetings. All that happens is that my colleagues schedule 15 minute long meetings in the gaps. It's exhausting.
I regularly schedule focus time or project time on my calendar and when I had days of stacked meetings, I’ll fill in the gaps with focus time to ensure I’m not overbooked.
I wouldn’t be shocked if there’s plugins or tools to help, though I do it fairly manually.
You can add a regular meeting for yourself too, instead of focus time, also set your calendar not to share meetings' details with other folks, so they will only see 'busy'