Apart from the obvious mappings, the URC-1280 has 2 spare buttons to cover 12 native buttons (Opt+, Prev/Replay, Next/Skip, Audio, Sub, Text, Slow, Sleep, V Fmt, Wide, Bmk, +Bmk), as well as 2 (Media, TV Portal) that can be reached in one step from Menu,
TV/Radio that no-one needs, and List that is covered by OK. Although it might be possible to teach the less used functions on spare, devices, I think OP has better options unless the OFA remote is in a skip.
Universal remotes have been discussed here before. It's not easy to find one that works well for the Humaxen (even without considering the
almost complete uselessness of Amazon's search function. The normal problems are that the Chinese ones overload the colour buttons while the US ones don't have colour buttons at all (some have A, B, C, D that could be painted) and generally the learning mode can't be relied on because of limited memory. Models that rely on proprietary external software for configuration inevitably die of bit-rot as the software's platform evolves and dies and/or the vendor's code library for the model becomes unsupported or inaccessible.