It's great that you've expressed your concerns. As you will see, all of them have a solution...
I would like to add an owned movie file with the title "T2 Trainspotting"
This movie is in the database with the title "Trainspotting 2". With the next update I'll add the aka "T2 Trainspotting". Thank you very much for reporting this missing aka, and feel welcome to use this forum anytime you see something that must be corrected.https://www.coollector.com/viewtopic.php?f=4&t=1065
this program does not allow to add movies with my own description
By clicking the description field, you can write your own description, write your own review, or write notes.
It's true the poster is the same for everyone, but when the poster is not good you're welcome to contribute a better one.https://www.coollector.com/viewtopic.php?f=5&t=55
I am totally dependent on the author's frequent (or in this case infrequent updates).
The database is updated several times each month, but problems that I'm not aware of won't get fixed magically. You have to report the problem to be sure it'll get fixed.
I was somewhere reading in this forum that you can search a missing movie with the IMDb number, but to date I am still unable to see this feature in this program, unless I am missing something very gravely here.https://www.coollector.com/help.html#title
You copy the IMDb Id (for example tt0111503) into the clipboard, then you paste it into the program (control + V).
My request to the author: Allow adding movies manually if a movie is not recognised by the program.
Otherwise the whole idea becomes very obsolete for me having a number of movies on my disk which cannot be catalogued.
Of course you must be able to catalog all your movies and series!!!https://www.coollector.com/viewtopic.php?f=5&t=116
This is the dedicated section of the forum where users request movies to be added. You could have found it by clicking the menu "Help->How to request a missing movie".
Please read our help page, you'll probably learn a ton of things