My personal favorite is Auxy. Has a subscription, but there's a ton of free instruments included so the subscription isn't mandatory. Very easy interface but can create complicated compositions. Can export to Ableton, MIDI, WAV and others. It's easily my most used app outside of Safari.

https://apps.apple.com/us/app/auxy-studio/id1034348186

I think the basic interface of Auxy would pass the grandparent test. Some of the knobs might be a little confusing. But selecting an instrument and plotting out the loops is dead easy.