Honestly, I'm not sure there's one magic tag for mxm on Wattpad. I've posted a few stories and noticed something weird—if I tag with just the obvious stuff like #mxm or #boyslove, it sometimes feels like I'm shouting into a void. The algorithm seems to pick it up, but then I get buried under the sheer volume. I started experimenting with pairing those with super specific trope tags, like #enemiestolovers or #royaltyau, and that's when I'd see a small bump in reads. It's like you need the generic tag so the right people can find it, but then a niche tag so you're not lost in a sea of other mxm stories.
I also wonder if Wattpad's sorting works against us sometimes. New stories with those tags pop up every minute, so unless you're getting immediate traction, you sink. I've had better luck using a character dynamic tag, something like #grumpxsunshine, alongside the main pairing tag. It seems to hook readers looking for a very specific flavor of relationship, and they're more likely to stick around and interact, which the algorithm loves. The whole thing is a bit of a puzzle, really.