Apologies for missing your post.
I have a Pi4 running the development branch:
osmc@osmc:~$ uname -a
Linux osmc 5.10.32-1-osmc #1 SMP PREEMPT Wed Apr 28 05:45:57 UTC 2021 aarch64 GNU/Linux
and wireguard seems to work – though I’ve not actually tested its connectivity.
osmc@osmc:~$ sudo ip link add wg0 type wireguard
osmc@osmc:~$ ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,DYNAMIC,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
link/ether dc:a6:32:b7:81:4c brd ff:ff:ff:ff:ff:ff
3: wlan0: <NO-CARRIER,BROADCAST,MULTICAST,DYNAMIC,UP> mtu 1500 qdisc pfifo_fast state DOWN mode DORMANT group default qlen 1000
link/ether dc:a6:32:b7:81:4d brd ff:ff:ff:ff:ff:ff
4: wg0: <POINTOPOINT,NOARP> mtu 1420 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/none
osmc@osmc:~$ lsmod | grep wireguard
wireguard 73728 0
libchacha20poly1305 16384 1 wireguard
ip6_udp_tunnel 16384 1 wireguard
udp_tunnel 28672 1 wireguard
libcurve25519_generic 40960 1 wireguard
libblake2s 16384 1 wireguard
ipv6 552960 33 wireguard
osmc@osmc:~$ grep -i wireguard /boot/config-5.10.32-1-osmc
CONFIG_WIREGUARD=m
# CONFIG_WIREGUARD_DEBUG is not set