@DJH
As I outlined in another thread, this area is very complex and may require the services of an accountant in order to get it right.
Consider this paragraph from a post in the Revolut community (concerning gains on Revolut Trading Accounts but applies just the same here imo):
In theory, when you receive dividends, if your “revenu fiscal de référence” is above 75k€ for a couple, you must, before the 15th day of the following month, fill-in the 2778-DIV-SD form and send it to your local tax office with a check worth 21% of your perceived dividends, as an advance you are making to the tax authorities. And do this every time you receive dividends. To be honest, my advice is that you can skip this and just declare your dividends of foreign origin once a year, you should be fine with this approach.
The full post/thread can be seen here
Note that the Revolut thread OP cautions that he is not a professional and accepts no responsibility if the advice is incorrect. He writes “This is my understanding and own interpretation, I cannot be held liable if you follow this and it is not accurate”.