Their value is based on nothing but algorithms and faith. A dollar doesn't actually represent anything. Even if you hold the physical dollar bill in your hand, in the span of 4 years of Biden's administration, its value can still decrease by 40%. You can't buy as much as you used to with it. It has no actual value. If an apocalypse or a Venezuela-esque bankruptcy were to strike, a 100$ bill would be worth less than a strip of toilet paper.

I agree that having the physical bill is worth more than going through the intermediary of Visa and Mastercard when they can block your account willy-nilly, or when other groups can choose not to recognize bank transfers from those institutions as valid. However, we are far past the point where our money had any true value beyond the abstract.