Bought a house cheaply. What now?

It depends on the location. The more attractive it is, the less I would invest financially before resale. I wouldn’t do too much anyway, as a buyer usually has completely different ideas.

The same applies to renting. What is the maximum realistic cold rent? If only 5-6 euros per sqm are common, then a renovation is not worthwhile. If there is also a restaurant in the building that might be leased out, this tends to have a rather negative effect on tenant interest. Most people just want their peace and quiet.

I would only do a basic renovation if a) I can rent it out well and/or b) want to move in myself later.

When reselling, you have to keep the speculation tax in mind. It is due up to 10 years after purchase.

Thank you very much for the reply. I will research the various questions. Yes, we are also considering moving in ourselves.

Yes, officially he bought it.

My advice to you is to just leave it that way. If he, as you say, likes to take risks (in this case pure gambling), he should do it alone. You will very likely be very glad someday that you never signed anything related to it.

The market value is higher according to the appraisal

He should just put it back on sale immediately and collect the "higher market value" right away. Even after deducting the speculation tax, he would have made a quick profit with no effort at all.
I fear, however, that he will soon realize that the "market value" will not be reflected in the current sale price. Do you know how many old pubs, hotels, company buildings, etc., so-called junk properties are waiting somewhere for buyers?

Of course we ourselves don’t know how it will end, and yes, profit motive was certainly involved

In the casino on red or black you have almost a 50% chance of winning. As soon as you put money in there without a solid plan, your chances are significantly lower and possibly one day a lot of money will be gone, which you wouldn't even have had to get from the bank for such a measure.

(the father practically renovated the family house alone at that time)

...does the father already know about his new job? Sons sometimes have a somewhat romanticized view of the scope of their father’s house renovation. And... the father can’t do that alone!
I don’t mean this in a bad way at all, but I strongly advise you to keep your hands far away from something like this, since you can neither even remotely estimate nor influence the consequences.

Always funny how here, without any background knowledge, people immediately make judgments about others instead of simply answering questions.

It’s always funny how here, without further background knowledge, people immediately make judgments about others instead of just answering questions.

Feel free to address me directly; I can handle it.
Freely following the proverb "who can read is often at an advantage," I have done so and therefore know that a woman is at least "somehow" involved in a completely unplanned house purchase (feels/is) and partly relies on evaluations from acquaintances with "little knowledge" for a property that apparently no one wanted to buy before.
Since she obviously – rightly so – is worried or at least seriously considering it, she wants feedback. Mine is honest, and I believe she is capable of accepting it. She probably needs fewer shoulder pats; they won’t be the ones paying the bill later.
Buying such a property and – by her own admission – with no experience at all, is in my opinion an absolute harakiri act, which is why I would immediately sell it (hopefully at market value).
There are partially experienced home builders and experts here; I cannot imagine that any of them would cheer the OP with a joyful "Well done" or "It will be fine," because they know the risk at least from their own long-planned and secured house construction.
Maybe I have already experienced too many similar scenarios that mostly ended in chaos; at least for me, all imaginable alarm bells are ringing with this depicted, completely unprepared project.
THIS is what I want to express with this and to encourage the OP to seriously reconsider.
It was not my intention to judge you or anything; for reasons I have experienced professionally many times, I wanted to clearly tell you that you should definitely let your boyfriend handle this gamble alone, because in my opinion, it is nothing else. Sorry if it came across differently to you; then I want to apologize for that.
I believe the facts presented by the OP are significant enough; still, thanks for your clear notice!

Crazy story. I hope your boyfriend has the necessary cash and income. Just don't take out a loan for him or sign anything.

would you like to post some photos?

P.S. Just a quick note about the inn. There is also a reason why it is no longer leased. Pubs and inns are always on the brink of insolvency by default, because amateurs often run them as a dream (not the proper restaurants). A longer vacancy often means that there will never be an inn there again. The conversion (change of use from commercial to residential necessary) usually costs quite a lot of money. Personally, I would never buy a property that is largely an inn. That almost always means stress and costs a lot of money.