Apart from this topic which offers a small variety of code scripts to use on Terminal, I thought using available apps would be more user-friendly.
The Finder in macOS can rename multiple files only if they are under the same directory as described in the "Rename files, folders, and disks on Mac" Apple support webpage but I would like to rename files in different directories. I don't really have the time or the energy to go through deep coding on Terminal to make changes to thousands of files.
So here is my solution in the answer section. Please feel free to comment/add any other simplified solution to rename multiple file (& filepaths) at once on MacOS.
Other app alternatives (haven't tried them yet apart from the one below).
find
with the-exec
option. No GUI will ever be as efficient and versatile as such a simple command. Moreover, it's an easy case to start gaining in skill.