Reverse ssh tunnel using openssh 8.6

Some time ago when I used openSSH 7.x and older kernels, creation of reverse tunnels or tunnels as such was an easy exercise. Now, with 8.6, I can't create any, all I get is the message:
Tunnel device open failed.
Could not request tunnel forwarding.

tunneling is allowed in both ssh and sshd configs at both ends.

there is additional message:
debug1: sys_tun_open: failed to open tunnel control device "/dev/net/tun": Permission denied

I understand that I have to allow regular user to open tun device, but how?
(Slackware64-current, openSSH 8.6)