I just solved the issue following this video. Using the command provided in solution 1 did the trick.
The command I used is the following:

sudo ln -s /usr/local/mysql/lib/libmysqlclient.21.dylib /usr/local/lib/libmysqlclient.21.dylib

The explanation of how this works is in that video, for anyone stepping with this problem in the future.
Thanks @jsulm for your help and time.

Hi, to get that missing the driver dll (ibmysqlclient.21.dylib) perhaps you have not installed MySQL on your Catalina PC? For more see here

Then please mark this topic as solved, thx.

@Christian-Ehrlicher said in building qsqlmysql.dll for msvc error:

Forgot to copy or typo?

I forgot to copy.
I looked into Makefile.Release and realised that instead of

C:\mysql\include

this It was including this

C:\Program Files\MySQL\MySQL Server 8.0\include

I deleted qmake.stash and config.cache and repeated the qmake again and this time I generated qsqlmysql.dll successfully.
Tested it with Sample Cpp code in Qt, it's working.
@Christian-Ehrlicher Thanks for the suggestion.

@jsulm
Thank you very much! This is exactly the problem, I set up mingw in the environment variable, which caused me to compile MSVC Qt using MINGW

No, you have to use the same compiler that was used to build Qt. You can't mix and match C++ librairies built with MinGW and MSVC.

@Sivamani-V said in How to connect to mysql server in ubuntu 16.04?.:

QMYSQL Driver not loaded. Available drivers: QMYSQL QSQLITE QMYSQL3

This gets asked so many times, here & elsewhere. Googling for your message will bring up many hits. Under Linux/Ubuntu it's usually libmysqlclient or libqt5sql5-mysql or similar which is missing/has dependencies missing/wrong version.

IIRC, if you start from the git clone. Why not use the archive corresponding to your Qt version ?

@JonB @MrShawn

Thanks you two for clarifying.

After downloading/installing a MySQL server in a school computer, I could build/run my app on my computer and insert/update data successfully to the server. That part's all good. Thanks from y'all.

Marking as solved.

Ok, thank You so much.
I will try to do it, tomorrow.

@koahnig

You're right, I think I'll go for it.

Thx for your time et your help anyway.

Hi and welcome to devnet,

Please search the forum a bit, I've already provided the solution several times for OS X/macOS.