Just adding my personal experiences of thonging in Bali. I’ve worn swim thongs in various public beaches and hotel pools and frankly most people don’t really care. The most you’ll get is a smile or a quick stare. A significant majority of women will also wear thong bikinis, covering up only with sheer sarongs when outside the beach or the pool in coastal areas. I’ve only seen one other male thonger in my years of visiting Bali, though.
To name a few, I’ve walked through the entire strech of Jimbaran, Sanur, Canggu, and Nusa Dua beach and had a pretty positive experience overall.