"Unable to write to wp-config.php" is usually a problem you get when installing wordpress on a linux environment. In my case, I wanted to install wordpress locally on linux with the the xampp apache server.
The error is related to the default linux unauthorised read and write or file permissions for that folder where you have your wordpress.
This is a quick solution to fix this issue
On your terminal run the following:
cd into your
htdocs where you have your
Next, change the user username and grouwp ownership from the default root:root to your own username and group
sudo chown -R yourusername:yourusername /opt/lampp/htdocs
Note: remember to replace "yourusername" in the command above with your own username and group. Most of the time, the username and usergroup is same words. e.g jovialcore:jovialcore
Next, change the htdocs folder and all files persmissons to read and write by running the following command :
chmod -R 777 htdocs