Euronext collectively is big, but Euronext Dublin is about 1/27th the size of LSE by its own market cap.

https://en.wikipedia.org/wiki/Euronext_Dublin

https://en.wikipedia.org/wiki/London_Stock_Exchange

That said, I'm not entirely clear how the exchange's market cap should or shouldn't be thought of in terms of the total market cap of assets that the exchange lets you trade. Or indeed the float of those assets, which is a concept I've only learned about due to SpaceX's nonsense IPO, so take my thoughts with an appropriate pinch of salt.