At https://uapi-group.org/kernel-features/#clock_monotonic-network-timestamps it says
Currently network timestamps are exclusively in CLOCK_REALTIME, even though for many (most?) a monotonic clock would be much preferable, as calculations become easier when one doesn’t have to think about clock jumps and similar.
At the-tcpdump-group/libpcap#1570 a user asked for support for CLOCK_MONOTONIC_RAW in packet captures. That feature would probably be most easily done by requesting CLOCK_MONOTONIC_RAW timestamps in AF_PACKET sockets.