Not sure if this helps, or not.  But this is the relevant part from a 
bash trace:

+ cmd nft -f /dev/fd/63
+ echo '[#] nft -f /dev/fd/63'
[#] nft -f /dev/fd/63
+ nft -f /dev/fd/63
++ echo -n 'add table ip wg-quick-wg0
add chain ip wg-quick-wg0 preraw { type filter hook prerouting priority 
-300; }
add chain ip wg-quick-wg0 premangle { type filter hook prerouting 
priority -150; }
add chain ip wg-quick-wg0 postmangle { type filter hook postrouting 
priority -150; }
add rule ip wg-quick-wg0 preraw iifname != wg0 ip daddr 192.168.150.14 
fib saddr type != local drop
add rule ip wg-quick-wg0 postmangle meta l4proto udp mark 51820 ct mark 
set mark
add rule ip wg-quick-wg0 premangle meta l4proto udp meta mark set ct mark
'
/dev/fd/63:5:76-80: Error: syntax error, unexpected saddr

^^^^^
Cheers.


On 1/1/2020 11:34 PM, Eddie wrote:
> Ha.  Even older:
>
> root@The-Tardis:~# nft -v
> nftables v0.6 (Support Edward Snowden)
>
>
> And in reply to a couple of off-list messages:
>
> wireguard-tools-1.0.20191226
>
> There are different reasons for using different VPNs.  Can you really 
> "totally" trust the one that you're using.
>
> Cheers.
>
>
>
> On 1/1/2020 10:22 PM, Edward Vielmetti wrote:
>> Eddie - what version of nftables does Slackware come with? The output 
>> of `nft -v` should be helpful.
>>
>> There is a report from stackexchange that nftables at 0.7 gives this 
>> error, but at 0.8.1 or better it's OK. I was not easily able to 
>> verify that from the source code, but it would be where I'd start to 
>> look. There was
>>
>> The nftables 0.8.1 release notes (from 2018) are here: 
>> https://lwn.net/Articles/744480/ and it points to new syntax in this 
>> release.
>>
>> good luck!
>>
>> Ed
>>
>> On Thu, Jan 2, 2020 at 12:27 AM Eddie <stunnel@attglobal.net 
>> <mailto:stunnel@attglobal.net>> wrote:
>>
>>     First time running wireguard as a native client on my Slackware 14.2
>>     system throws this:
>>
>>     root@The-Tardis:~# wg-quick up wg0
>>     [#] ip link add wg0 type wireguard
>>     [#] wg setconf wg0 /dev/fd/63
>>     [#] ip -4 address add 192.168.150.14/32
>>     <http://192.168.150.14/32> dev wg0
>>     [#] ip link set mtu 1420 up dev wg0
>>     [#] wg set wg0 fwmark 51820
>>     [#] ip -4 route add 0.0.0.0/0 <http://0.0.0.0/0> dev wg0 table 51820
>>     [#] ip -4 rule add not fwmark 51820 table 51820
>>     [#] ip -4 rule add table main suppress_prefixlength 0
>>     [#] sysctl -q net.ipv4.conf.all.src_valid_mark=1
>>     [#] nft -f /dev/fd/63
>>     /dev/fd/63:5:76-80: Error: syntax error, unexpected saddr
>>
>>     Fairly simple config to connect to my VPS:
>>
>>     [Interface]
>>     Address = 192.168.150.14/32 <http://192.168.150.14/32>
>>     PrivateKey = <Not the key you're looking for>
>>
>>     [Peer]
>>     PublicKey = <Just being overly paranoid>
>>     Endpoint = www.xxx.yyy.zzz:51820
>>     AllowedIPs = 0.0.0.0/0 <http://0.0.0.0/0>
>>
>>     Not sure what additional information you need collected at this
>>     point.
>>
>>     I'm able to connect outbound successfully using NordVPN's version of
>>     wireguard, but that doesn't use wg-quick, which is where the
>>     issue is.
>>
>>     Cheers.
>>     _______________________________________________
>>     WireGuard mailing list
>>     WireGuard@lists.zx2c4.com <mailto:WireGuard@lists.zx2c4.com>
>>     https://lists.zx2c4.com/mailman/listinfo/wireguard
>>
>>
>>
>> -- 
>> Edward Vielmetti +1 734 330 2465
>> edward.vielmetti@gmail.com <mailto:edward.vielmetti@gmail.com>
>>
>
>
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