Sorry about the slow response. I’m on holiday in a place with no mains electricity and patchy internet coverage.
Let-to-buy is a purchase plan the banks were offering a few years ago, and some developers too. It’s not generally something that private vendors offer, though curiously there is another thread on just this subject, where, if I understand it correctly, a private vendor has agreed to a rent-to-buy plan: https://www.spanishpropertyinsight.com/discussion/forum-topic/good-deal/
If you are looking for a let-to-buy I guess you should start with the bank real estate websites.
Where abouts in Spain are you looking?
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