That doesn’t sound like proper bircher muesli to me. Bircher is: soak oats in water, add grated apple, lemon juice, ground hazelnuts, “Kondensmilch” (like tubed, sweetened concentrated milk).
I usually do it as follows (but it’s not “Bircher”): Mix oats with soymilk, sugar and cinnamon. Sometimes I add a little joghurt to get a denser consistency. Then some fruit. Berries, grated apple or banana (in slices) work well. Mix and soak overnight. Eat cold in the morning. I usually also prep 3 portions and eat them over the next 3 days.
Throw in some chia seeds or ground flaxseed if you want to publish the recipe on a foodblog.
atool, wraps many archiver in one command
https://www.nongnu.org/atool/