Grouping by categories too big for visualization - Any tips?

Really like the way you can explore data in Metabase, but the one thing I can’t seem to get past is when drilling into a time series + customer or brand there are too many customers, brands for it to show the results.

Example: Looking at a high-level last month transactions, I see a spike in the last week of December so I highlight that week to drill in and then add a group by customer or brand and hit refresh. The visualizations don’t support more than 20 series of data so I get no results in the visualizations. I understand that showing too many customers, brands would make the graph unreadable, but how can I make that next step in exploration work. I am thinking I would need to drop the group by date and then go from there, but wanted to know if anyone else experienced this and have any tips on exploring data where you often group by larger catagories.