Mudita
Etymology
A Pali and Sanskrit term, "muditā," meaning "joy, gladness," central to Buddhist ethics as one of the four "brahmavihāras" ("sublime attitudes"). It is cultivated deliberately as an antidote to envy. English has no everyday single word for it, which is part of why it is often borrowed directly.
noun · /moo-DEE-tah/
Joy felt at someone else’s happiness or good fortune.
What it names
The generous gladness of delighting in others’ success as if it were your own.
Example
When her rival won the prize, she surprised herself by feeling genuine mudita.
Related idea
It is the exact opposite of schadenfreude: joy at another’s good fortune rather than pleasure at their misfortune.