This is not a performance question rather around theoretical future proofing.
I have 32GB ram in my PC I built myself and was considering buying another 32GB. I do some basic photo/video editing and also to reduce potential ram bottleneck (not that I know much about that).
My question - Is it worth buying more DDR4 ram now or is there potentially something else just around the corner (in the next few years) like DDR5?
Well, DDR5 will be out there within the next 12 months, but will be expensive and real life performance improvement in your use case will probably be unnoticeable.