I really like the Phosphor icons. They have a clean, modern look, a great variety, and they’re free and open source. Here are my suggestions for the icons that could work well for each section:
- Splits/Plans:
map-trifold(or other bullseye/target/map/route icon) - Workout Days:
calendar(or other calendar icon) - Exercises:
barbell(pretty self explanatory)
It’s not super original, but it’s easy to get.