Security Provider

Settings
Update and Security
windows security on left pane
Virus and threat protection on main windows
Manage Providers on right of main window
under heading
Who is protecting me.

I realise that is the point on which you actually asked for advice, but may I point out that if Malwarebytes is the premium trial - then by default it will show Defender turned off
When the trial expires and Malwarebytes become scan on demand only - then you can turn Defender back on OR of course you can cancel the trial on the GUI of malwarebytes and immediately go to scan on demand only, rather than waiting for the trial to expire.

IMHO I find malwarebytes somewhat of a nuisance these days when one tries to use the scan on demand only.
I have since 10 used only Defender and Malwarebytes ADWCleaner .

That is always scan on demand and one is never pestered to upgrade.

My Defender has only found anything TWICE since 10 in 2015
If it was to find something I would use Defender OFFLINE scan to check if there was anything that could not be found whilst windows was running.

I would then depending on what it was use ESET one time scan
Free Online Virus Removal | ESET

Cheers
You asked

However, that's not necessarily the problem. I cannot find the Security Providers page. I have tried to search for it, both through Windows Search and the Settings Search. Nothing comes up. Where can I find it?

So did you find it, from my reply

Settings
Update and Security
windows security on left pane
Virus and threat protection on main windows
Manage Providers on right of main window
under heading
Who is protecting me.

and on the one where the bank recommended it and gave a free premium code
WHO is providing the protection - quite part from the fact they are both turned on.

Re this
On other computers where Malwarebytes is only on the free version, my problem is that a major update requires you to upgrade to Primium trial, and only then can you turn it off. There is no way to install major updates without the Premium trial being initially set.

I do not know how long you have been using malwarebytes but this became common procedure when malwarebytes removed the ability to download/install ONLY the free version and changed so that you had to install the trial.

Further to the above I strongly suggest you need to read the guide from malwarebytes
Windows Security Center (Premium only)
Malwarebytes Premium and Malwarebytes Trial versions register as a security solution on your Windows device by default. If kept enabled, your Windows operating system recognizes Malwarebytes as your security solution. If you run any other anti-virus software, you may need to register that program with Windows Security Center separately.
https://support.malwarebytes.com/hc/...es-for-Windows


You need windows security centre as your provider - Defender
the fact that malwarebytes is also running does NOT mean that Windows security is your main security

Additionally if you set malwarebytes or allow it to stay set as your ELAM scan your computer will run slower at startup
You do need to read the guide
I have seen so many problems when malwarebytes has NOT been set correctly
NOT I must stress malware problems, but performance issues

Perhaps related
Computer Speed