Hello,
Yes, as mentioned, our “Fixed column” feature is currently not available for the Simple table type in any way.
In regards to your existing table, unfortunately, there is no way to ‘transform/change’ one table type to another one, especially with the Simple table – this table type is unique in the way how its data is structured, stored in our Plugin’s WordPress database, etc…
You would have to create a new table, choose “Create a data table linked to an existing data source“, such as a CSV/Excel/JSON/XML or PHP array and then you can use the “Fixed Column” option on it.
The only ‘workaround’ you can try, is to copy the cell values from the Simple table and try to paste this into any kind of Spreadsheet, like Excel or CSV.
Then you can make a table linked from the Sheet and use the Fixed Column feature on it.
If you switch to the premium version of our Plugin, of course, in that case, you would have some additional table types, such as the Manual table type, which can be editable from our Plugin and has some exclusive features for easier editing, such as the Excel-Like Editor view, but we are not allowed to discuss anything about premium features here, so if you require more details on that subject, you can open a pre-purchase ticket on our Main support, they will be happy to advise.
I hope that helps.