If someone remixes your track, usually the same splits of the original track apply on the publishing royalties for that remix (unless agreed otherwise).
Remixers are usually contracted by labels and artists under a “Work-for-hire” agreement and are provided with royalties on the master side and/or an advance fee. This means that you should upload the remix as a recording to the Work to receive the publishing royalties for that track.
For covers, you generally cannot earn publishing royalties on a cover song because the publishing rights belong to the original songwriter, not the artist performing the cover; you can only earn royalties for your unique recording of the song (master recording royalties) by obtaining a mechanical license to cover the song.
When you cover a song, you are not the composer, so you don't earn publishing royalties related to the song's composition.
If it substantially changes the original composition (e.g., changing lyrics or melody significantly), it might qualify as a derivative work. In this case, you would need to find out who is the Publisher of each of the original Writers involved and get their explicit permission to release the derivative work. If approved, you may share publishing royalties based on your contribution to the new arrangement