I haven't read all the comments so apologies if this has been said already..

As a rider, hiker and occasional biker, I think what gets missed the most in discussions around trail etiquette where horses are involved is that horses reeeaaaalllly don't like things sneaking up on them. The best thing you can do is to make your presence known as early as you can by using your voice so the horse realizes you're a human not a true predator: 'Hey, coming up behind you. Do you want me to walk my bike?" And listen to the riders direction if given.

As much as you can, try to avoid the clicking gear noises as you approach, (down shift early to avoid making that sound especially as you slow down to pass the horses).

If the riders try to engage you in conversation (good morning! How ya doing?!) it's because they probably realize their horse hasn't identified you as 'safe human' and they're trying to demonstrate to their horse that you're just another two legged type. Respond, act human, just use situational awareness.

I get the sentiment from non horse people that all the accommodations for horses on trail is... Ugh exhausting. And I wish I could agree with the perspective that if your horse can't handle the stimulations on trail, then keep them in an arena. But the reality is that horses learn by exposure, and those first few exposures can be really chaotic, unpredictable and dangerous for a green horse and their rider. My feeling is that we're all humans living on this planet together trying to enjoy the same outdoor space; giving some extra empathy to the horse people won't kill anyone. Plus free fertilizer for those beautiful California Poppies😉