Privacy and your data
Your runs, plan and settings live on your phone. Your account keeps a copy of your plan (its settings, its units and the days you have done), your profile, and your records, totals, trophies and weekly miles, numbers only. Sign in with Apple on a new phone, or after reinstalling, and those come back. Apple Health brings back your runs from the last 30 days, with the maps and heart rate it holds.
Everything else lives only on the phone, and iPhone backups of Why Not are off on purpose, so it is lost when you delete the app: runs older than 30 days in Activities, with their maps and share cards, every run's Read, the bell, your Settings choices other than units (voice, notifications and the rest), and your WHOOP connection, which you connect again.
WHOOP data stays on your phone for 35 days at most. The privacy policy, in Settings under ABOUT, says what Why Not keeps and why.