iMac loading slowly and My Passport backup drive issue

WD Passports with mechanical drives inside have a less than stellar record here for longevity. As they age, they tend to want more power to spin the disk motor than a computer's USB port can provide. As that is the only power available to run the drive, they can fail to mount.

The fix for that is to place a SELF-POWERED UBS hub between the drive and the computer. That kind of hub will have an independent power supply that supplements the power from the computer port.

However, this part of the message:

suggests that another drive, possibly the internal, is not happy.

The EtreCheck report that our wise Toad requests will better show us the drive and volume structures at play without revealing any personal or security information.

Please download and run Etrecheck.  The free version is sufficient. However, if you find it worthwhile you should support the developer and purchase the app.

Copy and paste the results into your reply. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

and after clicking on the Reply button use the Additional Text button to paste the report in your reply.

Then we can examine the report and see if we can determine the cause of the problem.

I've had some drive behave like that. What I do is manually unmount them and then apply the First Aid through Disk Utility. Give that a try.