Popular narrative that NEON does not have a move mask alternative. Some time ago I published an article to simulate popular bit packing use cases with NEON with 1-2 instructions. This does not include unpacking cases but can be great for real world applications like compare+find, compare+iterate, compare+test.
I am the author of the optimization of partial sorting and selection in Clickhouse. It uses Floyd-Rivest algorithm and we tried a lot of different things back at the time, read [1]
Overall clickhouse reads blocks of fixed sizes (64k) and finds top elements and then does top of the top until it converges.