If you were on master_2019.2 and had data in your database, loading master_2020 should not show these messages. Rather it would show you messages concerning the application of patches to the database.
Use phpMyAdmin (or other tool you use to access databases directly) and verify the you have data in your database. It sounds as though you don’t.
Note that the instructions given un Version Update Process say to backup up the database but not to erase it. Then the si2020Converter.php program simply converts your old custom.config.php file into the new custom.config.ini file used by the update. Verify that all the information for your database base that is now in the custom.config.ini file is correct (the same as it is in the custom.config.php except the field name on the left will have been updated.
If your database content was somehow lost, you can DROP all the tables and import the SQL file backup of your database you made in step 2 of the update instructions.
Now you can access the database and you should see a screen that says there are patches that need to be applied. And you go forward from there.