Block size
There won't be any. The previous hard cap of 64 KB minus packet overhead is dropped, since in the real world there are file records that are bigger than that.
Easiest example that comes close to that limit is here https://en.wikipedia.org/wiki/Torrent_file the file "debian-503-amd64-CD-1.iso" with "pieces" size of 51 KB.
Clients can still choose to not download blocks that are of excessive size, and clients are encouraged to keep block sizes small (at least smaller than 64 KB minus packet overhead) for efficiency (so that the block fits in a single UDP packet).
Howdy, Stranger!