I did set up iptables to work as nat and set up forwarding on the firewall. To reiterate it does work with windows but not either of my Debian computers.

Could you go ahead and post the output of

This Is a know working Debian 10 setup hope it helps you. Test setup only will not work after reboot and network-manager will break this every time link state changes. Was just using this for testing.

WAN="eno1"
LAN="enp2s0"

#
# delete all existing rules.
#
iptables -F
iptables -t nat -F
iptables -t mangle -F
iptables -X

iptables -P INPUT DROP
iptables -P FORWARD DROP

# Always accept loopback traffic
iptables -A INPUT -i lo -j ACCEPT

# Allow established connections, and those not coming from the outside
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -m state --state NEW -i ! $WAN -j ACCEPT
iptables -A FORWARD -i $WAN -o $LAN -m state --state ESTABLISHED,RELATED -j ACCEPT

# Allow outgoing connections from the LAN side.
iptables -A FORWARD -i $LAN -o $WAN -j ACCEPT

# Masquerade.
iptables -t nat -A POSTROUTING -o $WAN -j MASQUERADE

# Don't forward from the outside to the inside.
iptables -A FORWARD -i $WAN -o $LAN -j DROP

# Enable routing.
echo 1 > /proc/sys/net/ipv4/ip_forward

# Kill IPv6
sysctl -w net.ipv6.conf.all.disable_ipv6=1
sysctl -w net.ipv6.conf.default.disable_ipv6=1

ifconfig $LAN 192.168.0.14/28