PFIC rules apply to US persons (citizens, green card holders, US tax residents). An Indian-resident investor in a UCITS fund is unaffected. But the moment that investor moves to the US — for a job, marriage, citizenship — every UCITS unit they own becomes a PFIC under US tax law, with punitive annual mark-to-market or excess distribution rules.
If there is any meaningful probability of US residency in your future, holding UCITS is a deferred problem. Direct US-listed ETFs or IFSC AIFs avoid PFIC. This is one of the few cases where the right answer for an Indian-resident with potential US emigration plans is to avoid the otherwise-optimal UCITS structure.