The TPK file is not visible on the Linked Content tab because its spatial reference is not stated properly. It is possible to disable the spatial reference filter in ArcGIS Survey123 Connect 3.12 by clicking the 'Link content' button, and select 'Map package'. Click the 'Filter' button, and enable the 'Ignore spatial reference' option.
TPKX files are not supported on the Linked Content tab.