Thank you everyone for all your replies — it’s honestly been such a relief knowing it wasn’t just my iPad suddenly being too old for the ChatGPT app!!. 
I wanted to share what I’ve done so far:
I emailed support@openai.com directly (thank you to the user who suggested contacting support via both chat and email — I did both!).
The AI support agent who replied confirmed there are currently no widespread outages, but they believe this may be a new compatibility bug affecting some iPads running iPadOS 17 after the latest update.
They asked for additional details like iOS version and model, and whether the issue happens in both portrait and landscape (it does — still white), and whether I have any accessibility settings turned on (I don’t).
I’ve sent all of that information to them, so it’s now (hopefully) officially logged with the engineering team for review.
They also mentioned that regular app updates are released, so a fix for iPad-specific issues should arrive soon. (Hope so!)
For now, I’m using the iPhone app (works perfectly) and the Safari web version on iPad as a workaround. It’s not ideal tbh — definitely a bit slower and clunkier than the app.
Thank you again to everyone who chimed in here — your messages honestly stopped me from thinking my poor iPad was doomed!
I’ll post another update if I hear anything further.