I don't really like this kind of bonuses, mainly because it's hard to meet or complete the requirements.
All casinos hope you don't complete the wagering requirements. That's why they are there. 40x isn't that bad. I have seen 100 or 200x.
Also there's only specific slot game you can use those free spins.
That's also not out of the ordinary. Many casinos restrict you to a list of slots you can use your free spins on. Sometimes it's from different providers, other times it's some or all games from specific providers. Generally, they won't let you play games with the highest RTPs.
I prefer to have bonuses or free spin with no wagering requirement like the one I get when playing on Roobet. IIRC, I received free spins after wagering 8K and those free spins had zero wagering requirements.
All bonuses have wagering requirements. If they didn't, you would be able to convert the bonus credits to real money, wager with it as you please and withdraw it. But you can't do that. But there is such a thing as a no wagering bonus. That applies to the winnings. A no wagering bonus requires you to wager the bonus money the casino gave you, but you don't have to wager the winnings further.
Since you mentioned Roobet, they have a 35x wagering requirement:
12.4. You acknowledge if you opt into the 200% Deposit Offer you must wager your next deposit and the bonus coming with it at least 35 (thirty-five times) before you are eligible to withdraw. (Wager requirement of 3500%).
https://roobet.com/bonus-and-promotion-policy