Recently when working with a table in Azure SQL Database, I came across an issue that manifested itself in Power Apps in a few ways.
The message stated that the data source is read-only, when I knew that my SQL credentials had the correct permissions to insert and update table records. I was successfully doing this with other tables, so SQL was not the issue.
Attempting to use functions like Remove and Patch provided the message, as did Form.Edit.
The solution kind of makes sense after the fact but there’s no way I’d have guessed it.