Thank you very much for your helpful post chili,
it has been working for me a long time. But with the kernel update to 4.15.0-55-generic-x86-64 it stopped working, I tried to reinstall (after removing) using your instruction again, but failed.
Now I'm running 4.15.0-54 again, with no problems.
Hoping either the next kernel will work with rtl8821CU-5.2.5.3 or an other solution will be posted.