Do you think it is a good practice to inform the reviewers in-text about some changes reported in the revision report? If yes, how would you highlight the new additional elements? Is there a common practice?
Yes, I definitely think you need to tell the reviewers what changed. Normally, in math, we prepare a separate document explaining the changes. As a referee, I have sometimes seen authors also highlight any new text in red, which does make it a lot easier for me to check the new stuff without having to re-read all the old stuff. As an author, I've done this, too, but sometimes my co-authors think it makes the whole thing messier. Plus, it's a lot of mucking around in the latex file.
My new favorite way to deal with this, both as an author and as a reviewer, is an online PDF comparison tool, like this one: https://www.draftable.com/compare
As a referee, when I receive the new version, I use such a software to compare it to the old version. As an author, I might consider mentioning the existence of such software in my "response to referee" document, if there were lots of changes, and I want the referee to be able to quickly check them without re-reading the whole paper, but also don't want the hassle of making text red only to later turn it black again.
This process holds both for publishing a paper in a journal, and for a back-and-forth over a grant or research proposal.