Not protected by FINMA but, as I understand it, the main customer assets are held by IB LLC in the US where they are protected by SIPC (up to USD 500k total asset protection, cash protection limited to USD 250k). Some customer assets may be held by IB UK where they are protected by FSCS (up to GBP 85k).
Also, if you don’t borrow any money (margin) or stocks, all customer assets are segregated.