Skip apps. Use time based smart albums.
On iPhone, open Photos, tap Search, pick a year or month, then “Select” and drag your finger to multi select. Delete whole chunks from old years first. Most people never view photos older than 2 years. I’d start deleting from 2015–2019 in bulk.
On Android, use Google Photos. Filter by year, long press one photo, scroll to the end of that year, tap the last one, delete hundreds at once.