Based on this, “all the songs I’ve heard that were written in this century sound exactly the same”, I don’t think you’ve studied music history. That’s how music has always been.
There was a pop group in the 1930s-40s called “The Ink Spots”, they had 6 Number One hits, and many top 20. Every song sounded the same: nearly the same guitar opening, singer 1 with a line, then singer 2 repeats the same line in a deeper voice.
And the old people complained about it back then, same as today.
Teacher once told me to look up the spelling in a dictionary, and I spent the next hour looking at the dictionary, until she asked me what I was doing. I told her I was looking for the word and hadn’t found it
my grandmother had a big bruise on her arm. I asked how it happened, and she said “the wind!”