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While I cannot really determine what the cause behind your issues is, it might be related to the way the SDXC card has been set up. There are basically two ways to set it up: Portable storage (“external”) or Phone storage (“internal”). For more about this, see
While I and others here usually warn against opting for phone storage (for reasons see the link), some apps might actually not accept saving on a portable storage SDXC card, probably for data security and/or digital rights management reasons. The apps you mention might be such cases – perhaps intending to prevent you from “exporting” copyrighted content. It’s not clear whether the serious issues with phone storage that arose with Android 10 on various Fairphones persist, I for my part would still not risk and still refrain from the phone storage option (you mentioned saving photos which has proven a major issue with phone storage).