Riot Meddler notes they are refunding XP boosts next patch
/u/RiotMeddler posted on BlueSky:
Hey all. Given changes to League levelling rewards post 30 we'll be refunding RP spent on XP Boosts for players who had them active at the start of the Season and are in regions that support refunds. That will happen a couple of days after Patch 25.S1.S2 launches