Opening this here as a meta since it will affect all projects and not just one.
The rise in use of the Steam Deck as well as Linux gaming in general has revealed a long standing issue with the case of filenames. On Windows, filenames can be whatever mixed casing you want and nothing is affected by this. So up until recently, no problem.
Linux, and by extension the Deck, all have case sensitive file systems unless the user has gone to the trouble of installing one that supports case-insensitive names. This is definitely NOT the norm though.
Bethesda.net force all downloaded files to be in lower case. Since bethnet is a common means for Deck users to obtain mods, this generates a cascading problem with filename in general. Especially when mods begin to depend on other mods.
Going forward, all UPP projects should ship with all lowercase filenames. It might temporarily cause pain points with existing mods using it as a master but we'd hope that over time, anyone using it as such will incorporate the filename change in their master lists.
Oblivion may not be feasible due to the loose files issue. So unless an easy method for lowercasing all the assets being used by the UOP can be found, it may need to be set aside for this.