How to add a dummy code for (G)LMER

Dear R experts --

I never needed to add a dummy column and always query statistical results
by querying summary(model) for GLMER. However, I was recently asked to add
a dummy column for interaction variables when performing GLMER. Could
anyone tell me if it's necessary to add a dummy column for GLMER or R
automatically handles it when outputting results?

Best,
Yune