I thought this was a mod issue, but it's not. I figured out what's causing it. I'm posting it here, in case someone has a similar problem.
While my sims were swimming in the river at Mt. Komorebi, I could click on some of them, but not others.
It turns out that my sims can only click on a sim in the water if that sim belongs to a gender they can woohoo. This includes the sim themselves.
For instance, while in the water, a female sim who can woohoo men cannot click on herself or on her female friend, but she can click on a man in the water.
A female sim who can woohoo women can click on herself in the water and on her female friend in the water, but she can't click on a man in the water.
A female sim who isn't interested in woohoo with anyone can't click on herself in the water, nor can she click on her female friend, nor a man in the water.
I've tested it multiple times, and this applies only to the gender the sim is interested in woohoo with. Romantic orientation doesn't seem to have an effect.
I'm using the version of the Sims that's most recent on this date (February 1, 2026), and I play on PC.
To work around it, before I get into the water, I just change the sim's sexual orientation so that they're interested in woohoo with women and men, and then they seem to be able to click on anyone. When I'm finished with them in the water, I change their orientation back.
I hope this helps.