Hello Vinci68,
As you noticed, there was no plug-in to export textures imported by a user to a SH3T. Actually, I don't think anybody requested such a feature even if it could be useful at least for backups (but there are other ways to backup preferences and imported stuff).
As it's quite close to ExportToSH3F plugin, I just programmed the ExportToSH3T plug-in available here (it requires a Sweet Home 3D version >= 2.3).
Similarly to ExportToSH3F plugin, this plug-in adds Furniture > Export imported textures to SH3T menu item to Sweet Home 3D to create a SH3T file which will contain all the textures individually imported by the user. If needed, this SH3T file can be edited with the Texture Library Editor.

[Note: plug-in was updated on 03/04/2024 to fix Italian localization]