[SalesForce] System.debug does not output when written in trigger

I have the following trigger:

trigger HelloWorldTrigger on Account (before insert) {
    System.debug('Hello World!');
}

I checked that the trigger code is saved. Now I run the following anonymous apex:

Account a = new Account(Name='Test Trigger');
insert a;

After the anonymous apex is run I am presented with the log view (I am using Developer console here). So, in the log view I select Debug Only and hope to see the text Hello World!. I expect it to happen because my anonymous apex inserted a new record of type Account and hence the trigger should have run and output the Hello World!. But I do not see the text. What am I doing wrong here?

I will attach a few screenshots of the process described above:

Here is a similar question. It is telling:

In your debug level check in Apex code debug is set

So, I go to Debug -> Change Log Levels.. and I get confused: I do not know what exactly should I change here.

Another thing to do inferring from the question provided is to check the log size. I did not know how to do that, but the question tells:

its on debug log page. You will find the debug size in bytes. You need to convert them.

I am looking at the log page an do not see any debug size information there:

Help me, please. I want to see this Hello World! text in my log.

Here is the Trailhead module which I was learning before encountering the issue.

Here are the screenshots of me trying to tweak the debug log using the Setup:

After this I go to developer console and try to do the same things and getting the same result (no output is generated).