Theming the Administration UI in the new version is a lot harder as it relies more on JavaScript for rendering than FreeMarker templates in the old one. We're keeping the option to use the old interface around until this has been mitigated.
That said, we are now relying on PatternFly (https://www.patternfly.org), which allows quite some customization through CSS variables.
As for the authorization screens, these are out of scope for the changes we're doing here. But they will probably get pulled into their own refactor at some point.
For the most part I am also happy with Keycloak, but they could do a far better job documenting things, especially their language adapters. For example the "Readme" for the `keycloak-connect` Node.js package has a link to documentation, but that documentation fails to document anything around the package.
Likewise I had better luck once I understood OpenID and then treating Keycloak as an extension of that. I even ended up writing my own code to deal with the bearer token passed to our API, because I couldn't find anything. If anyone is interested I can share it, but it isn't anything amazing.
Most of my best help came from outside of the Keycloak support groups and instead reaching out to other people who use Keycloak.
It looks like Minecraft is already using Metal. LWJGL makes use of other low level APIs by means of BGFX, since version 3.1.0 (per release notes) and Metal is one of the current targets.
Looking at a running 1.15 Minecraft instance I see it is using lwjgl 3.2.1 and there a link to "net.java.openjdk.cmd/com.apple.metal", when I do an lsof.
