Here is the explanation my friend. Hope it’s clear enough
2023: 1 team ascends (11 team league)
2024: 1 team ascends (12 team league)
2025: 2 team ascend, 2023 team is relegated (13 team league)
2026: 2 team ascend, 2024 team is relegated (14 team league)
2027 and on: 2 teams ascend and the 2 teams that ascended 2 years ago (2025) are relegated (14 team league forever)
10 Current franchised teams do NOT descend, only reason to be kicked out is if Riot manually decides to. So basically every 4 years, Riot has the right to kick any org and replace it with someone else (Most likely teams that ascended during those 4 years and perform well will be highly considerated by Riot to replace current orgs who don’t perform)