Error: Can't open display: 0

Solved problem with executing this command

export DISPLAY=$(cat /etc/resolv.conf | grep nameserver | awk '{print $2}'):0

This command can also be added in shell initialization files, for example, .bashrc, .zshrc etc. Also make sure to allow public access of X server running in Windows 10. For VcXsrv, -ac option is most important because it allows public access. See this GitHub issue for more discussion Microsoft/WSL: Can't use X-Server in WSL2.

I encountered this issue after changing the version of my WSL Ubuntu distribution from 1 to 2. Using

export DISPLAY=$(cat /etc/resolv.conf | grep nameserver | awk '{print $2}'):0

was not sufficient. According to https://github.com/microsoft/WSL/issues/6181 I needed to reconfigure the firewall. This can be done by

• going to Advanced Security -> Inbound rules (admin permissions required)
• delete all rules for Vcxsvr
• restarting Vcxsvr, which prompts you to set Windows Firewall for this program
• allow all (or enough) access

After these 2 changes, the problem was solved.