Please provide a way to remove single avatar options

@florian,

You should add the CSS code in "Custom CSS code" textarea, it is located in Dashboard > Forums > Settings > Styles admin page.

For removing the "Specify avatar by URL" filed use the following CSS code: 

#wpforo-wrap .wpf-field-type-avatar .wpf-field-wrap > ul > li:nth-child(2) {
   display: none !important;
}

For removing the" Wordpress avatar system" filed use the following CSS code: 

#wpforo-wrap .wpf-field-type-avatar .wpf-field-wrap > ul > li:first-child {
   display: none !important;
}

If you want to remove the "Upload an avatar" field use this one:

#wpforo-wrap .wpf-field-type-avatar .wpf-field-wrap > ul > li:nth-child(3) {
   display: none !important;
}

Please don't forget to delete all caches before checking. 

Also please check out wpForo built-in Enable Custom Avatars feature. more info here: https://wpforo.com/docs/root/wpforo-settings/features/#custom-avatars

The last point: please note: all questions related to wpForo should be asked in wpForo.com community. Here we mostly support wpForo add-ons issues.