Preparing two PhD simultaneously? I was enrolled in a PhD at the Faculty of Science, and broke up "temporarily" after 4 years due to a horrible Professor, and restarted a new PhD at the Faculty of Engineering.

For the 1st university, I am still enrolled, but I do not have a formal PhD supervisor.

For the 2nd University, I have collected a huge amount of data which allows me to split the topic in two separated ones (Processing and Characterization).

Now the horrible professor has gone from the 1st university, and there is chance to get re-enrolled with a new Professor.

Would that be possible to re-enroll simultaneously in two PhD programs (Science and Engineering) and write two separate dissertations of my topic at the same time? or at least one main PhD and the 2nd one as "appended thesis" with an introduction chapter, methodology chapter + publications for the experimental part?.

The goal is to recover the 4 years of gap in my CV which has nearly destroyed my Academic career, rather than "collecting" a new title.
I doubt that it is possible. Getting a PhD is a full time job, and your CV will raise a lot more eyebrows if people see that you were doing two PhD at the same time rather than a 4-year gap.

A 4-year gap on your CV has not "destroyed your academic career". If you manage to complete your PhD, everything will probably be fine. Most "clocks" (e.g. "you can apply for this grant only if your PhD is less than X years old", "you can be a postdoc only if…" are based on when you completed your PhD, not your own age. I've known people who defended very old compared to the norm and they became established professors. Be prepared to explain the gap in interviews, but don't try to hide it with tricks.