I wouldn't sweat it - just focus on eating unprocessed food fiber or not
A single bowl of oatmeal with chia seeds gets you about halfway there. 2-3 tbsp of chia seeds has ~10-15g of fiber, mostly soluble fiber. Soluble is what you want for lowering cholesterol because it binds to bile acid, which means your liver has to use cholesterol from your body to make more bile. The oatmeal adds another ~4-5g and is largely soluble too.
After that you don't have far to go. Besides lentils and many beans, whole grains are really fiber dense, e.g., having wheat bread on a sandwich can get you another +6 just from the bread. Brown rice instead of white gets you 3-4 more. Weird grains like barley and bulgur have a bunch and go well in things like casseroles, chilis, etc. You'll also get at least some from whatever fruits/veggies you were going to eat anyway.
It is a lot compared to what most people take, but it’s not hard. Banana, orange, some broccoli, and you are close. Lentils, beans (lupini is great because it also has protein) here and there, oats, an extra fruit (pear is nice), berries, avocado, so many options.
But you need to be conscious. Most people need less starch and sugar and fat.
I poop 2-4 times a day. I know some people have a real problem going to the bathroom once a day… just eat more fiber folks.