After a theme park holiday near a beach, something like portaventura

[Crouchendtigermum]

But not exactly that
as been there but that was a really good holiday

Lake Garda Italy and Gardaland. Not been yet but booked to go later this year.

I was also coming to say Lake Garda. There’s an excellent water park as well as GardaLand.

Yas island , Abu Dhabi

Gardaland - Legoland waterpark inside

Canevaland

Movieland

Stay in Peschiera del Garda on the lake and you're 10 minutes by train to Verona too.

Thanks I did think of gardaland
is there an actual beach near by at the sea. It the lake ? And is it easy to get to Venice for a day trip
via bus excursion or train ?

Gardaland is on Lake Garda so not near the sea. Some of the campsites have created beaches though.

Venice is 1hr 30 on the train with an easy change at Verona.