Working with VLAN

Doing my first steps and trying to configure and understans how this works and seems found one tiny BUG:
Debian Bookworm
NIC card configuret for 2 VLANs native for data, .20 for MESA with Layer3 switch.

# The loopback network interface
auto lo
iface lo inet loopback

# Management interface
auto eno1
iface eno1 inet static
    address 192.168.4.50
    netmask 255.255.255.0
    gateway 192.168.4.1
    dns-nameservers 8.8.8.8 1.1.1.1

# MESA P2P interface (.120-.121)
auto eno1.20
iface eno1.20 inet static
    address 192.168.1.122
    netmask 255.255.255.252
    post-up sysctl -w net.ipv6.conf.eno1/20.disable_ipv6=1

Seems like its trying to reach a wrong folder during startup..
Note: Using POSIX realtime
sysctl: cannot stat /proc/sys/net/ipv6/conf/eno1/20/disable_ipv6: No such file or directory

the right place is: /proc/sys/net/ipv6/conf/eno1.20/disable_ipv6

If LinuxCNC fails to verify that IPv6 is disabled and looks for the script/path in the wrong place, that is rather a software bug, not an OS issue.