Currently, many Wikibase modules are implicitly desktop-only because they don’t specify 'targets', whether intentionally or not. As part of work surrounding T324723, the default 'targets' will soon change from [ 'desktop' ] to [ 'desktop', 'mobile' ]; as at least some Wikibase modules are definitely not suitable for mobile, we want to avoid this change applying to Wikibase, and explicitly add 'targets' => [ 'desktop' ] to all Wikibase modules that don’t already specify targets.
Later, some of these modules should be set to desktop+mobile after all, but that will be done separately, and with PM involvement.