We also need the "paste using the destination formatting" option for the iOS copy/paste menu. What has been the biggest issue for me, is that when pasting text from an outside source, the formatting of the pasted text might be off from the rest of the text, but I have no way of noticing it in the iOS app. Only when I open the sent email from the web browser do I see that the text I pasted is 1 or 2 font sizes larger than the rest.

Agreed 100%. I regularly write emails on my phone and the lack of formatting options in the iOS Proton Mail app is a regular issue.
We need basic formatting options (fonts, sizes, bold, italics, underline, bullets, numbering).

Definitely need at least basic formatting capability

Any time I want to format text in an email on my phone I have to open Mail in my browser instead. That's not a good experience.

I'd also like to add the ability to do things such as resize text in the mobile apps would be super helpful. Text retains formatting when pasted into the message body on iPad and then I have to go to the web app to fix it before sending which is super inconvenient.

YES!! Not having even the most basic formatting options renders the mobile mail app close to useless. Being able to read mails is nice, but I can't write any mails that I would actually want to send to people via the app.