GitLab Project or Group for version control of 2 subprojects in my thesis, which consists of code and the latex report? If I need to version control my thesis, which contains my latex report and code, should I create a Group with two separate projects (code and latex) or should I create one repository called thesis with two directories in the root (code and latex)?
For most cases, it doesn't really matter and you should do whichever one makes most sense to you.  There are, however, some exceptions.


One significant reason I know of to split the two is if one will contain a lot more data than the other (e.g., you might have very large image files for figures in your thesis or large output logs from your code), in which case you'll have a faster and nicer time managing the smaller repository much more easily if it's separate from the large.
Another reason to split the two is if you might want to later release the code but not want to encumber it with the thesis source.
Your professor might also have requirements for people they work with in order to promote code reusability, in which case you'd need to follow those.


There are probably other exceptions as well, but for most cases, either combined or separate is OK, and you can always do surgery on the repositories later if you change your mind.