Based on the OS and soft keyboard you use, I think you have different options, here is what I do:
I look for privacy friendly soft keyboards that suits my needs ( esp. languages), and then look at the feature that keyboard offers.
If the soft keyboard supports emoji input, not the fancy ones, but the ones like " ;-D :-/ " etc., these can be used as passwords, just pick several , maybe 4-6 that you’d like and remember. it easily gives you a relatively strong 12-18 digit password.
Beware not all soft keyboard can be used before first unlock, in that case, you might want to keep the “emojis” easy to remember so you can type it yourself for at least once every time you boot.
Also beware, the fancy emojis might not work as a password and can be keyboard specific, if you switch to other keyboard that might not work.