If you have a clone of the Linux kernel source tree, you just have to look at the history of the include/uapi/linux/io_uring.h file. From a quick look here: everything up to IORING_OP_POLL_REMOVE came with Linux 5.1; IORING_OP_SYNC_FILE_RANGE was added in Linux 5.2; IORING_OP_SENDMSG and IORING_OP_RECVMSG came with Linux 5.3; IORING_OP_TIMEOUT with Linux 5.4; everything up to IORING_OP_CONNECT is in Linux 5.5; everything up to IORING_OP_EPOLL_CTL is in Linux 5.6; and the last three are going to be in Linux 5.7.