Hi @Gollnast, Viktoria ,
According to my research and testing, unfortunately, there is currently no way to change the button text "Save" to "Submit" using JSON.
For this requirement, I would like to recommend you submit a feedback to our Microsoft SharePoint Feedback for your convenience. If this feature is in high demand, engineering team will consider to deploy this function in the future version.
Thanks,
Yanli Jiang
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