Since this just came up again on a different thread and we are now on the cusp of 6.10.0 stable being released soon(tm), let me just re-iterate the following:
The Template Repositories section of the OS is now removed in 6.10.0+ It is not coming back.
It is not a "feature" being removed, but rather a reflection of reality of how the system was originally designed (to support an App Store type interface) and where we have been since 2015 (an App Store type interface released). Template Repositories was always intended to be a short term solution.
Since 2015 and the introduction of Community Applications, a reasonable assumption is that 99.999% of users have never used the Template Repositories section.
If you are one of the 0.001% of users that is still currently using it, there are 2 completely viable alternatives listed in this thread (put the xml's into either /config/plugins/dockerMan/templates-user or /config/plugins/community.applications/private/myNameHere)
NOTE: another reasonable assumption is that of the 0.001% of the users who think that they are using it, 90% of them actually aren't.
The reason why it's being removed in 2022 instead of being removed in 2015 is because prior to 6.10.0 Community Applications was basically an optional plugin. In 6.10.0, while CA is still technically optional, the Apps Tab will always appear in the GUI and if CA is not installed then there is a link to automatically install it.
Community Applications does not force you to only use templates which are present within it, nor does it hinder you creating your own templates via "Add Container".