Germany

From my personal experience of more than 20 years in that field, waiting lists for new members are indeed a very odd thing. Usually it's the opposite, volunteer fire brigades will pester anyone who looks only remotely interested to please join right now, basically, in most places, you'll be handed a form and told where to sign faster than you can say out loud "I'd like to join" 3 times.

Unequal treatment of applicants, if done on purpose, would be very much illegal.

The things new members might have to wait for is getting fitted with personal equipment, delivery times have been a sad joke since the pandemic, I've seen people wait for more than half a year for a pair of new boots.