I think the problem is that the code of the Time Theme Pro plugin (probably based on the Time Theme from the same developer) wasn't completely and correctly updated to take into account the changes necessary to work on Elgg 2. One thing that probably causes the error is that Elgg JS code is no longer loaded in the page header but loaded asyncronously as AMD modules. Plugins should do it the same way. And in case a plugin relies on any Elgg core JS it will cause errors as the loading order is not necessarily the same if you don't define dependencies correctly.

Maybe someone can suggest a working alternative theme to you (unfortunately I can't as I have written my own theme for personal use based on the default Aalborg theme and never really tried any others on Elgg 2).

Or you might have to think about hiring a developer if you need a theme with specific features and a look you like but don't find one you like.

You could try out the Containers plugin (https://elgg.org/plugins/1211419). It sounds it provides the functionality you are looking for. I have never tried it myself though, so I can't say if it's currently working without issues on recent versions of Elgg (even if it says compatible with 2.2 not 2.3 it should work fine on Elgg 2.3 but you might test yourself).

Hello iionly !
Amazing !
It works as I want.
Thank you very much !
CV

This is not a default functionality. You need to consider access level - an bookmark might exist for a given URL, but it might not be accessible by another user adding it.
This can be done however. You will need to write event handlers and check bookmark's address metadata, and files can be compared by md5 checksum, you would probably need to add checksum as metadata when files are saved.

Hello Ismayil,

Thank you for your answer.
I thought I would have to use elgg_get_entities_from_metadata().
In fact, I would not be able to do that.
Shame !

Regards,

CV