I think they're generally intended for use in SPA/PWAs. I doubt the shadow dom is particularly crawler friendly. Also, they aren't great at SSR though some fr

I think they're generally intended for use in SPA/PWAs. I doubt the shadow dom is particularly crawler friendly. Also, they aren't great at SSR though some frameworks try to fix that. It would also depend a lot on how you were using/designing them. If you were using slots and putting content inside of a custom tag, and just using that tag for display concerns, SEO would be just fine, though you may lose some semantic markup points.