[Milhouse]

But I do not understand why I should use the Libreelec forum, if this addon works fine on LE 7.0.0.

That's for when you have problems in future, as you probably will.

The OpenELEC version of the Transmission addon will not work with these test builds, and it won't work with LE 8 (once released).

The only supported LibreELEC Transmission addon is the Docker version, and the LE forum is the best place for general LE support (ie. official releases, add-ons etc.). If the Doccker version of Transmission lacks particular features, or is not up to date, the best place to discuss that would be on the LE Forum.