I formally enrolled in 2005/2006 and at the time these things were definitely not in place in the fields I studied. There were some mandatory introductory courses but even with those you usually had a wide range of options and one of the requirements for moving on was literally just N "weekly hours for a semester" in total of courses (primarily lectures) with no further restrictions. If it said 20 you could spend 20 hours by attending 10 lectures for a semester or spread it out over multiple semesters or you could take courses including courses from other faculties if they didn't have any restrictions on them (you'd only need to demonstrate attendance which was often not recorded for lectures so the only evidence necessary was having enrolled in it - until the BA/MA switch happened and lectures would only be considered if you had written an essay or passed and exam at the end of it, which nobody did).

I ended up dropping out for many reasons including the move to focus on self-employment but part of it was that I passed the deadline for graduating under the old system and that the switch meant a lot of my effort had been for naught as I would have had to write dozens of essays about lectures I attended over the years and the combination of courses I picked didn't neatly fit into the required modules.

I was also active in the department's student group so I got to see how they adapted to the new system and a lot of it was literally just rearranging the existing courses into modules based more on meeting formal structural requirements than actually developing a coherent lesson plan. I acknowledge that this is likely more of a quirk of the Magister studies than Diplom or Lehramt (for teaching professions) which always were more structured even before the transition.

I did a BA in the UK from 2003-2006 and it was modular, as was every other university I looked at judging by prospectuses.

I personally prefer the modular system. In the traditional system (in the UK at least) you were assessed by final exams with more or less fixed content, so you actually had less flexibility to study what you were interested in.