The obstacle is not the value. It is the use of funds.
Most of the refusals we see have nothing to do with the property and nothing to do with credit standing. They have to do with a field on the application form.
Your bank knows the house. It is in their district, it is paid for, the value is beyond dispute. Ask for a loan for a kitchen, a roof or a solar installation and the conversation is done in twenty minutes. Say the sentence „I want to buy a flat in Alicante with it“, and the room goes quiet.
The reason is prosaic: many houses want to see residential use within Germany. A property abroad is, for the lending guideline, not a known purpose of funds — not forbidden, just not provided for. And what is not provided for is declined across the board, because no one in the house wants to take responsibility for it. The security is in Germany, it holds its value, and the case fails anyway.
On the other side stands the Spanish bank with the mirror-image problem: it cannot value, secure against or credit your house in Germany. It sees only the equity you bring.
This is where buyers lose money without noticing: they pay for the property abroad in cash from savings, because the equity release „did not work“ — and later find that financing an already paid-for property abroad after the fact is markedly harder than financing it at the time of purchase. The favourable moment does not come back.