UDP mtu is limited in VLC 3.0 to 1316, you can set the packet size on OBS side by setting the address to "udp://1.2.3.4:4242?pkt_size=1316"

Though, I rather advise you, to use "rtp_mpegts" as a container on OBS side, and on VLC side to use rtp://@1.2.3.4:4242 rather than using raw UDP. Be sure to use an even port number.

reference: https://forum.videolan.org/viewtopic.php?t=143484#p470409

My VLC version is 3.0.20. According to the answer above, the packet size and port number were changed on the server side, and the video was now viewable in VLC.

Modified pipeline from RTP server:

appsrc ! videoconvert ! videoscale ! video/x-raw,format=BGR,width=2448,height=2048,framerate=21/1 ! videoconvert ! openh264enc bitrate=2000 ! h264parse ! rtph264pay mtu=1316 config-interval=1 ! udpsink host=127.0.0.1 port=10002 sync=false async=false