Linux

Here's mine, if this helps? I have WireGuard running on an Alpine LXC on my LAN, and use it to connect back home. I can SSH to or use resources from any other machine on the LAN while connected. You'll need to amend the include rules to match whatever distro you're using (the paths will be different), and you can add whatever rules you wish under the LAN section to allow local access to the WireGuard 'host' for other services (eg SSH).

There's also a lot of useful info on the Pro Custodibus blog.

#!/usr/sbin/nft -f
flush ruleset

define pub_iface = "eth0"
define wg_iface = "wg0"
define wg_port = "51820"

table inet my_table {
	set LANv4 {
		type ipv4_addr
		flags interval

		elements = { 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 169.254.0.0/16 }
	}
	set LANv6 {
		type ipv6_addr
		flags interval

		elements = { fd00::/8, fe80::/10 }
	}

	chain my_input_lan {
		ip6 daddr fe80::/64 udp dport dhcpv6-client accept comment "Accept DHCPv6 configuration"
		udp dport netbios-ns accept comment "Accept NetBIOS Name Service (nmbd)"
		udp dport netbios-dgm accept comment "Accept NetBIOS Datagram Service (nmbd)"
		tcp dport netbios-ssn accept comment "Accept NetBIOS Session Service (smbd)"
		udp sport { bootpc, 4011 } udp dport { bootps, 4011 } accept comment "Accept PXE"
		tcp dport ssh accept comment "Accept SSH on port 22"
	}

	chain my_input {
		type filter hook input priority 0; policy drop;

		iif lo accept comment "Accept any localhost traffic"
		ct state invalid counter drop comment "Drop invalid connections"
		ct state established,related accept comment "Accept traffic originated from us"

		tcp dport 113 reject with icmpx type port-unreachable \
                comment "Reject AUTH to make it fail fast"

		# ICMPv4

		ip protocol icmp icmp type {
			echo-reply,  # type 0
			destination-unreachable,  # type 3
			echo-request,  # type 8
			time-exceeded,  # type 11
			parameter-problem,  # type 12
		} accept \
		comment "Accept ICMP"

		# ICMPv6

		icmpv6 type {
			destination-unreachable,  # type 1
			packet-too-big,  # type 2
			time-exceeded,  # type 3
			parameter-problem,  # type 4
			echo-request,  # type 128
			echo-reply,  # type 129
		} accept \
		comment "Accept basic IPv6 functionality"

		icmpv6 type {
			nd-router-solicit,  # type 133
			nd-router-advert,  # type 134
			nd-neighbor-solicit,  # type 135
			nd-neighbor-advert,  # type 136
		} ip6 hoplimit 255 accept \
		comment "Allow IPv6 SLAAC"

                icmpv6 type {
                        mld-listener-query,  # type 130
                        mld-listener-report,  # type 131
                        mld-listener-reduction,  # type 132
                        mld2-listener-report,  # type 143
                } ip6 saddr fe80::/10 accept \
                comment "Allow IPv6 multicast listener discovery on link-local"

                ip6 saddr fe80::/10 udp sport 547 udp dport 546 accept \
                comment "Accept DHCPv6 replies from IPv6 link-local addresses"

		ip protocol igmp accept comment "Accept IGMP"
		udp dport mdns ip6 daddr ff02::fb accept comment "Accept mDNS"
		udp dport mdns ip daddr 224.0.0.251 accept comment "Accept mDNS"

		ip6 saddr @LANv6 jump my_input_lan comment "Connections from private IP address ranges"
		ip saddr @LANv4 jump my_input_lan comment "Connections from private IP address ranges"

		udp sport bootpc udp dport bootps ip saddr 0.0.0.0 ip daddr 255.255.255.255 accept comment "Accept DHCPDISCOVER (for DHCP-Proxy)"

		# Accept all WireGuard packets received on a public interface
		iifname $pub_iface udp dport $wg_port accept
		# Accept all DNS packets from wg clients sent to a DNS server running on the same local server (i.e. if running DNS and WG on the same VPS). 
		# Doesn't seem necessary if the DNS is just on a separate server on the LAN.
		iifname $wg_iface tcp dport 53 accept
		iifname $wg_iface udp dport 53 accept
		counter comment "count dropped packets"
	}

    chain forward {
        type filter hook forward priority 0; policy drop;
        ct state vmap { invalid : drop, established : accept, related : accept }
        iifname $wg_iface oifname $pub_iface accept
        reject with icmpx type host-unreachable
    }

    chain my_output {
        type filter hook output priority filter; policy accept;
        # Accept every outbound connection
        }
}

table inet nat {
    chain postrouting {
        type nat hook postrouting priority 100; policy accept;
        iifname $wg_iface oifname $pub_iface masquerade
    }
}

# The state of stateful objects saved on the nftables service stop.
include "/var/lib/nftables/*.nft"

# Rules
include "/etc/nftables.d/*.nft"

I wanted to do the exact same thing and found this extremely helpful blog post.

It works with iptables, and not nftables though, I don't know enough about iptables and networking to translate it to nftables.

(web archive link because the blogger is migrating their blogs, and this one is currently unavailable on their site)

Dunno if this helps, but it sounds like you're trying to do something similar (?) to what's described in this article:

https://www.procustodibus.com/blog/2022/10/wireguard-in-podman/

They also have this guide:

https://www.procustodibus.com/blog/2021/11/wireguard-nftables/#point-to-site

Good luck!