This happens most frequently for Systematic Reviews, Scoping Reviews, etc. We typically do not allow tables that are more than 1.5 pages in length to appear in the main manuscript, so the content of such a table will need to be moved to a Multimedia Appendix.
If you want the references included in the main paper (which is what we would recommend), you should add a sentence like like "We included 278 publications [1-278]..." as close to the in-text mention of the Appendix/Table/Figure/ as possible. This is the preferred option.
As an alternate option, if there is no overlap between the references of the main text and those of the multimedia appendices, that is, if the references cited in the multimedia appendix do not appear anywhere in the main text and are only limited to the appendix, then these references can be entered as a separate list at the bottom of the multimedia appendix alone.
However, if there is any overlap (even of 1 reference) between the references cited in the main text and those cited in the multimedia appendix, then all references from the multimedia appendix would need to be added to the main reference list of the manuscript.