Hi @Pinoq ,
Do you want to use check boxes to update a choice column(not allow multiple choice)?
If so, I've made a similar test for your reference:
1)You need to set check boxes' Text to the choices one by one manually.
For example: my choice column's choices are:
Choice 1
Choice 2
Choice 3
Choice 4
Choice 5
2)set check box1's Text:
"Choice 1"
set check box1's OnCheck:
Set(varde,Checkbox1.Text);Reset(Checkbox2);Reset(Checkbox3);Reset(Checkbox4);Reset(Checkbox5)
//set variable based on the checkbox text, if you check one checkbox, reset others.
3)set check box2's Text:
"Choice 2"
set check box2's OnCheck:
Set(varde,Checkbox2.Text);Reset(Checkbox1);Reset(Checkbox3);Reset(Checkbox4);Reset(Checkbox5)
4)set check box3's Text:
"Choice 3"
set check box3's OnCheck:
Set(varde,Checkbox3.Text);Reset(Checkbox2);Reset(Checkbox1);Reset(Checkbox4);Reset(Checkbox5)
5)set check box4's Text:
"Choice 4"
set check box4's OnCheck:
Set(varde,Checkbox4.Text);Reset(Checkbox2);Reset(Checkbox3);Reset(Checkbox1);Reset(Checkbox5)
6)set check box5's Text:
"Choice 5"
set check box5's OnCheck:
Set(varde,Checkbox5.Text);Reset(Checkbox2);Reset(Checkbox3);Reset(Checkbox4);Reset(Checkbox1)
7)use formula like this to update:
Patch(test1,First(test1),{department:{Value:varde}})

Actually, I more suggest you use radio to update choice column.
The settings will be more simple.
You just need to set the radio's Items:
Choices(test1.department)
Use formula like this to update:
Patch(test1,First(test1),{department:{Value:Radio1.Selected.Value}})
//test is my list name, please replace with your listname.

Best regards,