There are three types of freewheel for the enviolo, the old one saggy circlip version (pre 2018 ish?) obsolete and prone to damage, then an updated three spring freewheel with a circlip to hold the sprocket on and a nice noise, that replaced that older design.

then 2024 has a threaded locknut for the sprocket…its retrofitable to earlier models.

Gates belts drive sprockets fit either one of the other, so check for that…..chain sprockets all work,

a fairly simple fit if you’re dexterous and tidy..

Also fits Nuvinci N380/330/360 and all Enviolo hubs