I worked in tech until my mother was diagnosed, so I brought 25 years of IT when I started dedicating my life to understanding this disease and supporting her. I also helped set up and trialed some leading-edge solutions in a private care home.
You're on the right track. In this particular matter, what you need to do is the following:
a) set up a tablet with no particular sensitive information, no lock, no nothing, not even face recognition
This is because at first the patient will be able to use and login the tablet, but over time, they will lose interest in screens and you will rely on cognitive stimulation staff to present the tablet to your loved one.
b) link it up to a dummy account that you set up for the purpose of this exercise.
This is because you cannot expect any care home or nursing staff to do this for you, find pictures, relevant content, and culturally relevant information that could help support your loved one. Their job is to operate it, nothing more.
c) mirror the content using another device.
This works on both Google and apple ecosystem,s so that's 99.999% of tablets out there. Upload new pictures regularly. Upload movies to a Dropbox account and notify the care staff of the location of that folder. Install Spotify, and create playlists remotely so they can be played back locally.
I also recommend you install games (paid games, not free to play, as progression will not be sufficient to keep your loved one motivated). Things like puzzle games, memory games, etc. Make sure everything works offline (over time, the care home might disable or change the wifi password).
And very, very importantly: regularly remind the care staff that this tablet MUST be used as part of the cognitive stimulation program in their institution. Make it clear to the management if you have to, because staff changes over time, and this important tool might get lost in the staff rota.
PS: I understand my answer must sound highly regimented and a bit of a 'strange' response. But trust me; it's based on 7 years of experience with this illness.