The world of data security & privacy is a murky world where even the most innocuous detail can say a thousand words. So whilst you've committed to using an Omerta Phone, decided to stop using 1234 as your password, cast Google to the kerb & said Ciao to Facebook, have you considered your keyboard?
Predictive text is a fantastic invention, enabling clear and concise communication via screens which are woefully inadequate for typing. However, predictive text works by learning your writing style and memorising your grammar. After a few weeks of using a predictive keyboard, the internal dictionary is a literal gold mine to anyone wishing to know more about you. Key terms you use will show up constantly to anyone using your phone to send a quick text for example.
Whilst anyone using my partner's phone may be forgiven for thinking she is more than slightly lascivious, what would someone think if they were using your phone? Would keywords which might be considered incriminating or break commercial agreements be prevalent? If so then you might want to consider some strategies for combating this.
Signal offers an "Incognito" keyboard which saves nothing thus preserving your privacy. You can access this by opening Signal & going to settings>privacy. You can also edit the default GrapheneOS Keyboard from within Settings.
The bottom line is, this may not be a security concern for many people, but in a minority of cases it could be a serious issue which you have never given any thought to. Maybe it is time you did & act on your new found knowledge!