Hello @Anonymous and welcome to the community!
I'd like to help with this issue regarding objects that cannot be selected. The reason you cannot select those objects is because they have been XReffed into the scene as an "Xref Scene". If you go to the location shown in the image below and click the Xref Scene button as shown, you have an option in there to merge your objects into the current scene. You may find this more convenient in this case. Once you do that, you can select and manipulate them as normal. I hope this helps and let me know if you have any questions.
EDIT: Whoops, forgot to attach image.
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Best Regards,