Binary Logistic regression - Interaction containing more than 2 groups

#1
Hello,

I am running an Interaction which contains more than two groups, for example, the day of the week (monday, tuesday and so on). When this Interaction is created with another IV (covariate), should this day_of_the_week variable be set as categorical?

I looked online, a lot of blogs ignore this categorical feature, because the IV only contains two groups, for example, Gender (male and female). I understand that completely. But, what if the IV contains more than two groups. Should I mark this Covariate (which will be interacted afterwards) as categorical first, afterwards Interact this variable with another covariate variable or not?

Can you discuss your answer by explaining, why not, or why yes?