The design has been working perfectly from 2018 till today.

https://old.reddit.com/r/Monero/comments/1h6e4nk/randomx_5_y...

Most miners use AMD Ryzens. Couldn't tell you the actual breakdown of CPU types in use. Apple's M series CPUs are quite efficient at it too. Bitmain now sells a "Monero RandomX Mining ASIC" which is just a bunch of RISC-V cores, seemingly based on Sophon SG2042 SOCs. There's nothing special or more cost-effective about their product.

You can mine on old smartphones quite easily. I use a bunch of old Android TVboxes myself. Their hashrates are nothing to crow about, but their hashes/watt are still competitive with faster CPUs.

There is a RandomX V2 that will be deployed soon. Its main improvement is even cheaper verification cost.