Anytime I open my mail app it won’t open into the mailbox or inbox, invariably it’ll show a blank screen or a random email from ages ago…is there a way for it to open directly into the inbox?

Should go straight in I lie, it always go to the last email in the inbox, no idea if you can get it to open the inbox..will investigate. Tends to get confused if your using IMAP & edit your inbox from elsewhere, so the last mail it opened, has been delete Though worth check with your provider that the settings are upto date (& that your device is added as known device within the account security settings), if they are then maybe delete the account detail & re-add them afresh..

Is this just a UI issue?

It opens at the last email you were reading. The sidebar for the inbox appears if you press the little “< Inbox” link at the top left, or just view it in landscape format and the Inbox sidebar will always be there.

Ok, hadn’t known about the landscape display…or just not noticed it 😳

..swipe left to right on the email, will display you inbox in portrait mode