y ~ predictors that I am not interested in + (1 | group)

I would like to plot the predicted probabilities for each group. However, using the “conditions” argument in conditional_effects() is not possible, as I have no variable for the “effects” argument.

How to code a plot showing probabilities for each group?

Sorry, short on time, so just a very general pointer: it is often useful to interpret model via their predictions, e.g. using posterior_predict. This gives you a lot of choices about the details of what you are interested in. I discussed some of the choices at: Inferences marginal of random effects in multi-level models