Every Chromebook model I've ever had has had a physical switch or screw that can be removed/toggled somewhere on the motherboard to unset the write-protect bit.

e.g. https://joshuawoehlke.com/wp-content/uploads/2018/07/dell-31...

Some Chromebooks do have a physical switch, like in the battery compartment. I don't know of any Chromebooks where it's actually impossible to enter developer mode.