RE: Auto Scheduled Backup entire Business Central SaaS Database Daily
Outside of exporting a copy of the database using the admin tool (which you mentioned the limitations of), you're required to use the API. However, the API's biggest limitation is bandwidth (only about 2 MB/sec, up to 5 parallel calls). Also, a very limited number of tables are natively exposed via API, meaning you will have to generate new API endpoints.
My suggestion would be to setup a delta-load process using something like Azure Data Factory or Azure Synapse, load it to either a database or Azure Data Lake, and take a daily snapshot of the data from there.
Getting full database backups every day is not feasible with the current limitations. I'd ask your management team what they really care about and why. Is it for reporting? Restoring data? What data? For how long? How much data? etc.