I assume most or some of them are just random bytes to increase nonce space in the block header. Changing the coinbase affects txid, affecting merkle root.
Discussion
That makes sense. Thanks Jack.
I think I’ve learned that the weird characters are produced by taking hex bytes and using UTF-8 to produce Unicode which has some really crazy stuff far down the list. And this is the standardized way of reading op returns. Interesting!
You can put any byte in that space, but when they are being displayed for example on a block explorer web page, it often will decode the value as ASCII or Unicode since it's usually a human readable value. So random bytes will display weird Unicode mappings.