Underscores have a specific meaning in layouts as they indicate that they are a aublayout.. see the default blog layout for an example of what I mean. So I would suggest it is expected behaviour that a file with am underscore is not displayed as an available layout.

@brianteeman
Yep thought that might be the case with underscores. But the inability to select a Layout Override in Content Options and in a Category should be there even if there is an alternative Menu item Type for it.

not sure but that part sounds like an existing issue that we have a PR for testing see #16755

It may be linked but I think it is a separate issue. Creating a Alternative Layout menu item for a Category blog Override prevents the blog override being selected. But The same is not true for an Alternative menu Item of an Article Layout Override. I will test with the patch for the other issue and see.

This one looks like it's going to be complicated.

Addendum
Have tested the patch for the other issue and it has no affect on this issue. But it looks like it is part of the same issue

Closing in favour of #16755

Set to "closed" on behalf of @franz-wohlkoenig by The JTracker Application at issues.joomla.org/joomla-cms/16926

closed as stated above.

Is not a bug because see also #9464

@Webdongle

Steps to reproduce the issue
Create a Layout override for Category Blog

I dont know your Issue 16926 come from the same bug as is noticed in the Pull Request(PR) 16755.
PR 16755 is a new feature and sollution to make it easy to use an
Alterative-Article-Layout-Override
in a article-category-list-menuitem

This Alternative Layout is working for the view of a single Article
(view after if you click on a article of the article-category-list)

In PR 16755 it is only a little inconsistence of the "Alternative Layout for Article"-field.
But the rest works as expected.

But if i understand your issue right do you want a Alternative-Category-Blog-Layout-Override.

A quick solution for this:

Version 1:
This for a category of articles in alternative-blog-view:
After you have make a correct override (without xml-file) in templates/templat_name/html/com_content/category/
then you can go in backend to:
Content -> Categories -> (yourCategorie) -> Options -> Layout - select your Alternative-Layout-Override
for this categorie and save it. It make for me no sense to have an xml-file for this because the view comes from the categorie and not from a menuitem how works with the xml.

Version 2:
This for a Alternative Menu item Type for category of articles in blog-view:
After you have make a correct override (with xml-file) in templates/templat_name/html/com_content/category/
then you can go in backend to:
Menus -> (yourMenu) -> New -> Select -> Articles -> (yourOverride)
to create a menuitem with this Layout.

Version 3 :
If you need the same Layout for both then you can make two layouts(copy)
one layout with xml and one without xml with the "same" in it.
For example:
my-blog-layout-duplikat.php
my-blog-layout-duplikat.xml
my-blog-layout-duplikat_children.php
my-blog-layout-duplikat_item.php
my-blog-layout-duplikat_links.php

my-blog-layout.php
my-blog-layout_children.php
my-blog-layout_item.php
my-blog-layout_links.php

Version 1:
This for a category of articles in alternative-blog-view:
After you have make a correct override (without xml-file) in templates/templat_name/html/com_content/category/
then you can go in backend to:
Content -> Categories -> (yourCategorie) -> Options -> Layout - select your Alternative-Layout-Override
for this categorie and save it. It make for me no sense to have an xml-file for this because the view comes from the categorie and not from a menuitem how works with the xml.

But the problem is that once an xml file is created then the option for that layout disappears in categories.

your version 2 ... same But the problem is that once an xml file is created then the option for that layout disappears in categories

Your version 3 same But the problem is that once an xml file is created then the option for that layout disappears in categories

@Webdongle

But the problem is that once an xml file is created then the option for that layout disappears in categories.

This is intended read #9464
Version 1 is an alternative-category-blog-layout-override (without the xml-file)

Your version 3 same But the problem is that once an xml file is created then the option for that layout disappears in categories

You dont need this in categories because you have the self layout in the files and can choose
my-blog-layout

If you created my-blog-layout.php then you can copy this file to my-blog-layout-duplikat.php
similar with
my-blog-layout_children.php
my-blog-layout_item.php
my-blog-layout_links.php

Notice:
my-blog-layout-duplikat
is the alternative-catergory-blog-layout-override
that you can select as an menuitem and have then the self layout as in
my-blog-layout