If I want background music I just turn the volume down. There are some bands/singers who probably aren’t ideal as background music at any volume but most music I believe can work in a different way played at a lower volume.
The only purpose I can see of background music is to mask undesirable noise that otherwise would be intrusive or distracting. For that any pleasant but not interesting music of limited dynamic range would do - but what fits with that for one person likely wouldn’t for others.
To my ears, all the music I like - rock, prog-rock, classical, tragic opera etc - is easy listening! The “genre” of “easy listening” music, from what I have heard of it, is music to either cause either instant sleep or trigger a desire for rapid anaesthesia if not euthanasia!
I think Internet radio is ideal especially jazz and classical, and RP Mellow Mix.
It will play all day.
Some easy listening stations can be chosen and periodically you can swop stations for a little variety.
Background to what? First things first - I am a retired lawyer, so work was mostly reading and writing. I continue to read and write in retirement.
Writing: Classical guitar is the most reliable. But Baroque music (non-vocal and not Bach) and classical era chamber music often work.
Serious reading - Classical guitar is best. When maximum concentration is required, I have to turn off the music entirely.
Light reading (mysteries and such) Almost anything classical or jazz other than English language vocal music.
I also love watching baseball with the TV sound turned off and almost any non-vocal classical music turned up. Haydn is probably choice No. 1, partly because he composed so many enjoyable works and for me he fits the baseball season.