BabylonJS can’t be used with TS 4.0. During compilation several errors like this will appear:
error TS2610: 'isCube' is defined as an accessor in class 'Texture', but is overridden here in 'RenderTargetTexture' as an instance property.
Typescript 4.0 introduced a breaking change: Breaking Changes · microsoft/TypeScript Wiki · GitHub
It would be nice if this could be fixed. Currently i have to patch the .d.ts file manually.