Ask HN: How to get more experience with system design questions (esp scaling)?

Hi HN, I've recently gone through a few interviews where I did poorly on system design questions like "design twitter." The interviewers expressed a wish to see me go more in depth on technologies, but I simply don't have much experience in any of them, as my current role is heavily ML focused and issues of scaling were long-ago solved by my large employer. My question is are there any recommendations for ways to get more experience on system design? For most things it'd be as simple as "start a project revolving around X" but for scaling.. you kind of need users first. Was wondering how to get around this problem. Thanks