Did you have any chance to solve your problem? I might find your problem while reviewing the API document. As you can see below, the 30000 limit comes from the Kobo side not from the Power BI side, I believe what you need to do is you need to split you data set into 30000 batches, and import each one and merge them in the Power BI. can you check and let me know?
https://eu.kobotoolbox.org/api/v2/assets/{formuid}/data.json/?start=0&limit=30000
https://eu.kobotoolbox.org/api/v2/assets/{formuid}/data.json/?start=30000&limit=60000
https://eu.kobotoolbox.org/api/v2/assets/{formuid}/data.json/?start=60000&limit=90000
https://eu.kobotoolbox.org/api/v2/assets/{formuid}/data.json/?start=90000&limit=120000
https://eu.kobotoolbox.org/api/v2/assets/{formuid}/data.json/?start=120000&limit=1500000
