Church PowerPoint backgrounds that keep lyrics readable

Use a JPG still as a slide background, or an MP4 loop as a video background, in PowerPoint or Keynote.

A still as the slide background
Insert the JPG, send it to the back or set it as the slide background, and put your words on top. Designs carry no text of their own.
A loop as a video background
In PowerPoint, choose Insert, then Video, then This Device. Send it to the back and set Playback to Loop until Stopped. Keynote has a matching Loop setting. Menu names vary by version.
Backgrounds, not templates
These are background images and loops. They do not include slide layouts or editable templates, so you bring your own text and layout.
Pick a size
Use 1080p for almost every projector and screen. Choose 4K only for a 4K display and a computer that plays 4K video.