After a fresh installation of influxDB without creating a database and a user I get that error: "InfluxDB database is not accessible due to '401: {"error":"authorization failed"}'. Please check that the database, username and password are correct and that the specified user has the correct permissions set."
I tried that twice with d complete restart of HA (2026.5.4) in between.
Not an expert on this, but this seems like the problem.
You said you don't have the database or user set-up, the integration can't find the database or user...
If I am correct you have to use an App or whatever means to set up a version of influxdb. Once it's running use InfluxDB - Home Assistant to connect HA to it. Again, not an expert here.
What giidelines/instructions are you following? Are they up to date?