After installing WordFence plugin and setting up the firewall I experienced an interesting issue. All the images on the website disappeared and showed me the broken image icon.
When right clicking on the broken image icon and selecting view image in new tab, the result was Internal server error 500, not the image.
How did I solve the broken image / internal server error 500 after Wordfence install?
Turned out WordFence had installed .hctaccess file in uploads folder that was causing the issue and blocking anything from running in uploads folder.
Solution? Delete the .htaccess file from yourinstallationdirectory/wp-content/uploads
If anyone knows how to edit the .htaccess so that it still defends the site and remains in place, please comment below.
Btw there can be a lot more issues causing 500 internal server error on the whole WordPress site, see https://wordpress.org/support/topic/wordfence-causes-500-error/