This is something we are newly seeing on Onyx and Obsidian installations with Centos 7.8, but the issue might also apply to other OS. I have already filed a bug report on it, but wanted to share it here, too, because most likely others will come across the same issue soon.
Bug reported here:
The current work around is to create a database "manually" and then enter its credentials into the database (db name, user name) fields of the WP Toolkit installation page. When you do so, the Wordpress installations works fine as always.
Bug reported here:
Forwarded to devs - WP Toolkit error: Database credentials not working on installation dialog when the database does not yet exist
User name: Peter Debik TITLE WP Toolkit error: Database credentials not working when the database does not yet exist PRODUCT, VERSION, OPERATING SYSTEM, ARCHITECTURE CentOS 7.8 Plesk Onyx with latest MU WP Toolkit 4.10.0-4072 PROBLEM DESCRIPTION Previously no issues on the machine...
talk.plesk.com
The current work around is to create a database "manually" and then enter its credentials into the database (db name, user name) fields of the WP Toolkit installation page. When you do so, the Wordpress installations works fine as always.