Unity has WebGL export support, and they're currently working on WebGPU export, as evidenced by their participation in the WebGPU spec process. Unreal Engine had experimental WebGL export several years ago, but it was dropped, and there is currently no official web export support.

Tim Sweeny has complained about Apple's "walled garden", and has promoted browser-based game streaming platforms like GeForce NOW as a way to circumvent Apple's Fortnite ban. WebGPU has recently reached the stable channel of Chrome, with Safari and Firefox having announced that they have begun the implementation process. With WebGPU becoming broadly available, a web export for Unreal Engine may have become more technically feasible, and may have opened up another way for Fortnite to side-step Apple's fees.

If the support is available in the editor, but is still experimental, this market will still resolve YES. If it has been announced but is not available in the editor, this market will resolve NO.