Tolkien did sell the film rights, but was very clear that any adaptation needed to be as accurate to his works. Tolkien once received a script for a adaptation of Lord of the Rings, but was deeply unhappy with how inaccurate the script was to his original work (see letter 210). This adaptation was never made because Tolkien rejected it. The letter was brutal and even the smallest changes (Théoden having an audience in a private chamber for example) was criticised and rejected by Tolkien for not being true to the world he crafted.
This Amazon series is fan fiction because it's not based on a novel that Tolkien wrote. It doesn't understand the themes he wove into his writings. It doesn't understand the world at all. It's cosplay. Fan fiction. A cheap imitation of Tolkien. The writers have arrogantly said they want to create the story Tolkien never wrote, but at the same time they disrespect the source material and the intentions of the artist.
First of all, I completely understand your point of view. But the era was not the same. Nowadays, the gender and race of the characters are reversed, the chronology is lengthened, etc. Tolkien is also an Englishman of his time, between two centuries. He would obviously never have accepted everything that happens today, and not only for his work. Worse, some people would call Tolkien a "bigot" (*cough* Resetera).
The difference is that Rings of Power takes place in a period where there is a great need to fill in the gaps. Unlike LoTR where the scenes were literally copied from the books.
Today, PJ's trilogy is revered, but I remember very well the time before Fellowship came out, a lot of people thought it was going to be crap, long before Twitter. Then, purists criticized Legolas for surfing on stairs, the Lothrian elves at Helm's Deep, the marshmallowy ending that replaced Tolkien's fears of industrialization, etc. But now the streaming platforms are doing so much crap that everything done before 2005/2010 seems to be perfect in comparison.
Of course it's a fan-fiction, Tolkien is dead and we're not going to see philologists and linguists writing such complex fantasy like him. You have to take the series as it is... up to a certain point, that we'll see when it comes out. Not to mention the amount of money spent on a series becomes absolutely ridiculous.