Open listening port while vpn turned on and hotspot tethering turned on

Phone root status: False Here is my ifconfig output in termux:

~ $ ifconfig
Warning: cannot open /proc/net/dev (Permission denied). Limited output.
lo: flags=73  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  txqueuelen 1000  (UNSPEC)

rmnet_data0: flags=65  mtu 1500
        inet 10.239.133.81  netmask 255.255.255.252
        unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  txqueuelen 1000  (UNSPEC)

tun0: flags=81  mtu 1500
        inet 26.26.26.1  netmask 255.255.255.252  destination 26.26.26.1
        unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  txqueuelen 500  (UNSPEC)

wlan1: flags=4163  mtu 1500
        inet 192.168.43.1  netmask 255.255.255.0  broadcast 192.168.43.255
        unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  txqueuelen 3000  (UNSPEC)

As you see there is interface named tun0. I tried open listening port such as web server that binded to tethering interface in my android.

python3 -m http.server --bind 192.168.43.1 --port 8000

In laptop that connected to android which has IP 192.168.43.150, I tried to access the web through browser http://192.168.43.1:8000 . It didn't successfully returning response. But if I turned off VPN which remove tun0. It successfully returning response in my laptop browser. What happened?