I export my 1h30 video from Lightworks, but the file after has 1 kb of data and doesn't open.

Welcome to the forum.

The file you're looking at isn't a video file. but a .lvix data file that Lightworks uses, as free user, your export video will be a MP4 file.

Since this isn't a bug, I'm moving this to a suitable section.

Please use a meaningful title eg "export file has data"

It says it's a MP4 file in proprieties though, I tried it multiple times but it still is a MP4 with 1KB.

Hello,

I assume you run Windows.

When exporting to Youtube or Vimeo format, Lightworks creates a tempoary file in system Temp (on Windows by default on system drive), even when exporting to file system. After export is finished, the temporary file is copied to destination and deleted. If your system drive hasn't enough free space to keep the entire temporary file, a valid destination file will never be created (the file is there, but empty). As far as I can remember, there's no error message if this happens.

I don't say that this is the problem in your case, but it's worth checking free space on drive C:.
If destination is on C: as well, you need to double the free space needed, e.g. for a 90 minutes video (in 720p Vimeo/Youtube format) make sure having at least 10 GB of free drive space before starting export.

The aforementioned .lvix files create Lightworks at clip import time. Before the extension, the file name also contains .mp4, at least if the imported original file is an mp4 file.
Example: Name.mp4.lvix
If your file browser hides the file extension, then you only see Name.mp4, even though it is not an mp4 file.

Before exporting, set the folder where the file should be exported. After finishing the export you should see a confirmation which contains a link to the exported file.
Example:

If in doubt, check whether the file date & time corresponds to the export time.
Does the automatically created filename match the name of your exported sequence?