Tx3g subtitles The subtitle type font cannot be forced in QuickTime player in the last macOS 26 version. It is constantly reset to Helvetica Neue. But WebVTT solves this problem. Subtitles are played on the selected font without difficulty.
Subler doesn't work well enough for WebVTT subtitles, and can't add it automatically. I expect you to think about it and your positive or negative answer.
External .vtt files are not automatically added in batch mode, and also language codes (.en) are not recognized in manual mode.