Impeller renderer is about 100 KB [0]. You still need to add things like text layouting library and image codecs to that size. A few MB in total I guess, but much less than a full web engine.

While Flutter could be used to draw UI to texture, Impeller could also be used by other UI frameworks. Recently, Avalonia team experimented with replacing Skia and a Flutter developer asked, if they are interested in using Impeller and even offered some help [1].

This would probably be suitable, as a more lightweight alternative to WebView, for integrating into game engines.

[0] https://chromium.googlesource.com/external/github.com/flutte...

[1] https://www.reddit.com/r/dotnet/comments/1nv3snm/comment/nh7...