https://coconuts.co/jakarta/news/indone … -marriage/
Indonesia's Constitutional Court says no to interfaith marriage
A case brought to the CC was rejected so the laws regarding same-religion marriage stay in place. The upshot is, if you want to marry here, you must be of the same faith as your partner.
Of course it's perfectly legal for expats to convert for marriage but take no part in religion. It's unlikely to be an issue at all with the possible exception of friction within the marriage if your spouse gets serious about their faith and demands you become active.
It happens.