(Sorry for contacting you again on RetroSpring, I don't know if you're still active on Reddit and I don't have Twitter) Every release of Altra64 hosted on the repository by Suprapote claims 64DD games don't save, is this the correct version of Altra64 for 64DD saving?
The menu version I'm currently using is already some sort of flavor of Alt(ra?)64 (I'm not entirely sure which), it at least boots 64DD cartridge ports