Barcelona Boqueria opening days and hours

Noting La Boqueria is one of the 39 municipal fresh food markets in the city, it'll be open on the 23rd and the 24th until 8:30pm, but not the 25th and 26th.

Not just that, you can also "monitor" how busy it is in real-time: https://ajuntament.barcelona.cat/mercats/en/

As a side note, Dec 26 is a public holiday in Catalonia, celebrating San Esteban (Sant Esteve/St Stephen) and it´s a very big family day, when families meet for lunch to eat canelons, a type of rolled pasta similar to canneloni, stuffed traditionally with the leftovers of Christmas lunch...or whatever the cook fancies, normally pork. Expect many places to be closed (except the touristy ones).

Yep... and for more info: https://www.bizflats.com/blog/what-is-the-day-of-sant-esteve

Checked out article linked to by Enric And fell about lauging when I read this: "In the UK, Saint Stephen’s day is also a national holiday and is most commonly known as Boxing Day on account of the traditional sports matches held on this day."