New XAMPP security concept:

Access to the requested directory is only available from the local network.This setting can be configured in the file “httpd-xampp.conf”.

1st step go to below path

/opt/lampp/etc/extra/httpd-xampp.conf

2nd step add below code

<Directory "/opt/lampp/phpmyadmin">
        AllowOverride AuthConfig Limit
        Order deny,allow
        Allow from all
        Allow from ::1 127.0.0.0/8 0.0.0.0 \
        fc00::/7 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 \
        fe80::/10 169.254.0.0/16
        ErrorDocument 403 /error/XAMPP_FORBIDDEN.html.var
        Require all granted
</Directory>

Next to restart the server

sudo /opt/lampp/lampp restart

Now successfully open phpmyadmin