Short answer: fewer editors than you would think. Native WebM export sounds standard until you go looking for it.
- Most editors export MP4 and expect you to convert afterward. - Open-source editors are usually friendlier here than the commercial ones; check your specific version, not a two-year-old forum post. - The reliable fallback: export MP4, then convert with HandBrake, Shutter Encoder, or FFmpeg. Works every time, total control over quality. - Do you actually need WebM? For your own website, yes, the file sizes are worth it. For YouTube or social, no, they transcode it themselves.
Match the effort to the destination. Do not gold-plate a workflow nobody asked for. And if your real goal is short clips rather than file formats, ReelCut delivers platform-ready vertical shorts with captions for $4.99 a video.