Can UK citizens connect through Madrid at the moment?

I am looking to book the following itinerary (after May 17th):

London, GB -> Madrid, ES -> San Jose, CR

Pretty much all options are with Iberia Airlines. The layover is around 1.5 hours, at most 2.

I am getting conflicting information from various sources on whether transit through Spain is allowed at the moment.

UK GOV website verdict: OK ✔️

Where permitted, transit times should be no more than 24 hours. Travellers must be able to present a negative PCR, TMA or LAMP test taken within no more than 72 hours prior to arrival into Spain.

Transit through Spanish airports to destinations outside the EU/Schengen area is currently permitted for flights departing or returning to the UK. Travellers must remain airside and be able to a present a negative PCR, TMA or LAMP test

Iberia Airlines Guidelines verdict: not OK (?) ❌

Enter Spain in the search box -> More Info -> Connecting Flight Information

There are some transit restrictions in Spain which are detailed below:

Only citizens and residents of EU or Schengen states, Andorra, Monaco, the Vatican City (Holy See), or San Marino; or holders of a long-stay visa issued by an EU or Schengen state, may transit Spain in order to travel to their country of habitual residence.

The UK is no longer part of the EU or Schengen states so this seems to imply that I cannot take this flight? Then again, it is also talking about returning to a country of residence, which I am not doing. The language used in that information panel is a bit unclear, so I may be misinterpreting it all.

Calling Iberia to ask - verdict: OK ✔️

I spoke to 2 separate agents on the phone who both said that as long as the layover is less than 24 hours it will be fine. They also said that if the final destination (Costa Rica) does not require a negative test result then you won't need it for the connection in Madrid either.

I cannot find any official Spanish government sources, but that may just be due to my poor Spanish. I have even tried calling the Spanish Consulate in London but it seems to be impossible to reach a person.