Hi and welcome to the forum!
Open the templates, save them as ODF template (.ott). You can then import them in the Template folder by using the File>Templates>Organize>My Templates, then Commands>Import template.
Please add
[Solved] at the beginning of the title in your
first post (top of the topic) with the
edit button if your issue has been fixed.
LibreOffice 7.0.3 on Xubuntu 20.10 and LibreOffice 7.1 (portable) on Windows 10.