Hi Hamish,
Welcome to BuddyDev.
Thank you for asking it. I had posted the code somewhere but could not find it on the forum, so posting again. Please put these codes in your bp-custom.php

1. Let us write a function to create a category with group name and save it as bcg category for group(you won’t need the code you have used in the above post)

/**
 * Create a Category with group name and set as BCG category
 * 
 * @param type $group
 * @return type
 */
function bcg_custom_create_group_category( $group ) {
		
	$cat = wp_insert_term( $group->name, 'category' );

	if ( ! is_wp_error( $cat ) ) {
		//insert it to group meta for blog categories
		groups_update_groupmeta( $group->id, 'group_blog_cats', array( 0 => $cat['term_id'] ) );
		
		return array( 0 => $cat['term_id'] );

	} else {
		//is it existing
		$term = get_term_by( 'slug', $group->slug,  'category' );
		if (  $term ) {
			
			groups_update_groupmeta( $group->id, 'group_blog_cats', array( 0 => $term->term_id ) );
			
			return array( 0 => $term->term_id );
		}
	}
	
	
	return false;
	
}

2. Let us Create the category and setup it when the group is create

//Blog Categories for Groups, auto category creation and association
function bcg_custom_create_group_name_category( $group_id, $group ) {

	bcg_custom_create_group_category( $group );
}

add_action( 'groups_created_group', 'bcg_custom_create_group_name_category', 10, 2 );

3. Disable the Blog Categories screen on Create Group and Grou Admin settings page

//modify extensions to hide the create/manage screen
function bcg_custom_modify_extension( &$extension ) {
	
	 $extension->enable_create_step = false; // enable create step
	 $extension->enable_edit_item = false; // If 
}
add_action( 'bcg_created_group_extension', 'bcg_custom_modify_extension' );

4. Modify the BCG form to add a hidden field and set post status to publish(we will use hidden field to set the forced category)

function bcg_custom_forms_args( $args ) {
	
	$args['tax'] = array();
	
	$cusom_fields = isset( $args['custom_fields'] ) ? $args['custom_fields']: array() ;
	
	$group = groups_get_current_group();
	
	if( empty( $group ) || empty( $group->id ) ) {
		return $args;
	}
	
	$cats = bcg_get_categories( $group->id );
	//if there is no category set
	if( empty( $cats ) ) {
		//create if not exists
		$cats = bcg_custom_create_group_category( $group );
	}
	
	if ( empty( $cats ) ) {
		return $args;
	}
	
	$cusom_fields['_bcg_selected_category'] = array(
		'type'		=> 'hidden',
		'default'	=> $cats[0],
		'label'		=> ''	
	);
	
	$args['custom_fields'] = $cusom_fields;
	$args['post_status'] = 'publish';
	
	return $args;
}
add_filter( 'bcg_form_args', 'bcg_custom_forms_args' );

5. Set the Category

//set default categorywhen post is being saved
function bcg_add_default_category_to_post( $post_id ) {
	
	$post = get_post( $post_id );
	
	if ( ! $post ) {
		return ;
	}
	
	$custom_fields = isset( $_POST['custom_fields'] ) ? $_POST['custom_fields'] : array();
	
	if ( empty( $custom_fields ) ) {
		return ;
	}
	
	if ( ! empty( $custom_fields[ '_bcg_selected_category'] ) ) {
		
		$term_id = absint( $custom_fields['_bcg_selected_category'] );
		//i know there is a loop here that can allow other categories to be asosciated too
		//to avoid that we need the group id in future
		wp_set_object_terms( $post->ID, $term_id, 'category');
	
	}

}

add_action( 'bsfep_post_saved', 'bcg_add_default_category_to_post' );

That will do everything.

It will remove the screens and auto set category name as well as set category for posts.

Please do let me know if that works for you or not?

Thank you
Brajesh

Hi Hamish,
You will need to translate using languages file.

Hi Hamish,
Please upgrade both the plugins.
https://buddydev.com/plugins/bp-simple-front-end-post/
https://buddydev.com/plugins/blog-categories-for-groups/

Also after upgrade, Please make sure to visit Settings->BCG Settings and configure it.

Now, coming to your issue:-
1. That is correct, I did not provide any hook to remove that. Please add following code to remove it

function bcg_remove_checkbox() {

	if ( has_action( 'bp_before_group_settings_admin', 'bcg_group_disable_form' ) ) {
		remove_action( 'bp_before_group_settings_admin', 'bcg_group_disable_form' );
	}

	if ( has_action( 'bp_before_group_settings_creation_step', 'bcg_group_disable_form' ) ) {
		add_action( 'bp_before_group_settings_creation_step', 'bcg_group_disable_form' );
	}
}
add_action( 'bp_init', 'bcg_remove_checkbox' );

3. Upgrading front end post plugin and the blog categories for groups will fix the issue.

Please update the code and plugins and let me know if that works for you or not?

Thank you
Brajesh