As the title, really. There's a BBC news article about it here: www.bbc.co.uk/news/uk-53687740
The article mentions a rise in cases in France, and looking purely at case numbers, The Netherlands seems to be following a similar pattern to Belgium. I would guess that they would be the next to be added to the quarantine list if things continue as they are.
Is this the start of a second wave in Western Europe, or is something else going on?