Thanks for the answer and for your time, although it is quite possible that this was a bit of a wasted time as there are no references to the questions of my post. But perhaps my question has not been very precise. Well, my point is that someone who has the phone model mentioned in the topic, wrote how much really free memory is available for data storage (because the system usually takes part of the pool).
The second question concerned the requirements of 4K movies, theoretically it is 70 Mbps, i.e. about 30 GB per hour of movie, which theoretically gives over 3 hours of recording on this phone (depends on the answer of previous question). It's even too much for me, especially since you can rip everything to the cloud at the end of the day. Nevertheless, the opinion of a practitioner would be very valuable to me.
Regards!