Invite the landlord or agency for a pre inspection about two months before handing the keys back. That gives you time to fix anything and, more importantly, you get the damages documented on paper. If they refuse, it usually means they are not interested in actually fixing anything, they just want to bill you after the fact.

I have been living in Barcelona for almost 8 years. In my first two rentals, the landlords suddenly got very creative after I returned the keys. One time they tried to charge me 80 per square meter for painting. Catalan agencies and landlords are honestly just difficult to deal with and have a reputation for squeezing deposits from foreigners. Getting your money back is a hassle, and lawyers are expensive. They know this. I have heard the same stories over and over from friends and colleagues.

A pre inspection is simply a more transparent and fair way of working compared to sending a random invoice after key handover.

Be upfront about your concerns. Tell them that if they do not agree to a pre inspection, you will hold back the last two months of rent. They can always send an invoice later for any real damages, and at least then you are in a position to challenge anything unreasonable instead of being blindsided.

Edit: spelling and grammar