I use GoodNotes for my studies and often have to summarize texts / papers or analyze them with regards to specific topics. What would be really helpful there if you can mark and associate specific parts of the text (e.g., some words, a sentence, etc.) with a chosen term ("tag" / "code") and have a view where you can filter for all of the passages marked with that tag. Researchers use that similarly for qualitative data analysis with dedicated programs (see for example: https://atlasti.com/2017/03/16/make-best-codes-atlas-ti/). However, an app combining convenient hand-written notes and coding seems not to be on the market - maybe that would be something for you? ;)