Can't change shutter speed on my DSLR?

I'm on manual mode on my Nikon 3400, but I can't change the shutter speed to slower than 60 and this yellow icon shows up, what does that mean? The icon on the upper left, below the big M

A 60th of a second is already very slow, in exposure terms.

The camera must be on a tripod, for longer exposures, to avoid image shake / blurring.

Thumbs down? Strange.
The symbol on the screen clearly shows a camera mounted on a tripod!

Why not go out on a limb here and READ THE MANUAL?

Hand-holding below 1/60th is difficult, as Robert J has already pointed out.

You're in Manual Movie mode, not Manual!

You're in movie mode which fixes the shutter speed. The icon is a movie camera (think old school film movie camera) on a tripod.

As Frank states, you are in movie mode. If you read your manual about movie mode you'll find out that the shutter speed can't be slower than the frame rate. I take that back, the manual is a pathetic piece of junk which tells you very little about how your camera operates. Nikon should be ashamed of that manual. Anyway, you can't set a shutter speed less than the frame rate as noted in better written Nikon manuals.