I want to get used to new slots, but I don't want to spend money right away. I see that not all casinos have a normal demo mode, and in some it is completely hidden. Is there a place where I can safely spin demos without authorization and investments?

Yes, there is — almost all slots are available in demo mode at Pin Up App Moreover, you can launch demos even without registration. This is cool if you just want to test the mechanics or try something new. I often use this function to choose a slot for a bonus — first I spin the demo, then I play for real. It works stably, both on a computer and on a phone.