I've built quite complex applications (e.g. a spreadsheet app) using SolidJS as a base layer, and in that sense it scales really well. It's very easy to separate data management from the UI, so architecturally it scales well, and performance-wise we rarely had issues with it at all.

The biggest issue is in finding people to work with it. If you're hiring React developers over web developers, they will probably struggle more with SolidJS's differences from React, in part because they just look so similar that there's more to "unlearn". But most web developer (i.e. anyone who can understand beyond just the confines of their favourite framework) should find it relatively easy to understand what's going on.