Much of the supply chain for modern hobbyist holography was sourced out of Russia, and the ongoing wars have made those materials unavailable.
There are some newer processes out there, but there were probably thousands of us that grew up using those HoloKit holography kits distributed by TJ.
That's required because off-axis display holograms have spatial frequencies ranging from about 1200 line pairs per mm for transmission holograms to maybe 5000 for reflection holograms.
Because the grain size is so small, these plates tend to be pretty insensitive to light. That's why they have limited use outside of holography these days.
Other types of emulsions such as dichromated gelatin also exist but are also hard to find. DCG is even less sensitive to light.
In either case, the wavelength the material is sensitive to matters when exposing with a single frequency laser.
Then there are issues about the substrate if the emulsion is on film related to polarization preservation.