Replacing 3-way dimmer switch with 3-way switch
Three way switches (dimming or not) have a common terminal and two traveler terminals. The common terminal of one switch in the pair is connected to the hot source and on the other switch, the common is connected to the fixture.

On your dimmer switch, the common is the reddish colored screw on the bottom of the first picture. It has a loop because it is the source of the hot, and the other wire is feeding another part of the circuit.

The other two wires on that switch, black and red, are the travelers.

On the non-dimmer, the common terminal is plainly marked. It has a black wire. The white and red wires are travelers. The white wire should be marked as black (marker or tape) because it is a hot line. It is acceptable to use a white wire for hot if it is marked.

You can easily swap out the switches. Just make sure that the wires that are now common are on the common terminals of the switches when they are swapped. And mark the white as black.