I installed KMyMoney using the software responsitory on my fresh Linux Mint 19.2 (MATE) install.
I believe it is version 5.00. It is NOT 5.07.

When I tried to open my existing database ("Open Database") it gave me the error:
If you want to use a database, you need to install some software first.
There was a CANCEL button and a HELP button, which leads to the entire Help file for KMyMoney. Not exactly helpful.

I did a search for "Database" and it only touches on the topic briefly. In short, it doesn't solve the simple problem of, "How does one install the needed software, and what software is needed to begin with?"

I installed SQLite, QT4, etc. but I'm still getting the same result.
I even compiled version 4.99+ of that weird sounding library, mentioned in the release notes of a recent version.

I wish I knew the exact package(s) that KMM was looking for. Anyone know offhand?

That depends a bit on the software you used to create the database. Currently, SQLite and MySQL (probably also Postgres) are supported as database backends. Which packages it needs for the database backends also depends on the distro you are using. Also, some Qt database glue libraries need to be installed. On my openSUSE system they are called libQt5Sql5-mysql and/or libQt5Sql5-sqlite. Two things are sure though: Qt4 is not needed since KMyMoney 5.0+ requires Qt5 and the weird sounding lib (Gwenhywfar) is not related to your database problem at all.

Hope that gives you a few hints.

It seems that libQt5Sql5-mysql is not a dependency of kMyMoney in ubuntu. I had to install libQt5Sql5-mysql manually.