Hi Keagan,
Thanks for coming back with me.
As per the updated details you have shared with me, it seems like the project is having a quite lengthy timeline. If so, as per my test results and searched in Microsoft Documentaries, currently there do have no out-of-box features in Project Online to zoom in the Gantt view and control them to get exported as the PDF in the same page.
From my further tests for you just now, if you are now have two split pages, I think a manual workaround may be take a screenshot when select the Page view to Two page and then crop the middle part to make the timeline connected. But I do understand this is low-efficient for end users especially for multiple split pages. But I do agree the timeline zoom out feature is indeed necessary to export the PDF as sometimes the entire project can be lengthy. And I suggest you submit this great idea directly to the Project Online development team and let the engineers get informed of this real customer requirement and improve this in the coming updates. You can do this by clicking the Smile button from your project and click I have a suggestion.
Meanwhile, I will make sure to keep your thread open and see if our community Project MVPs here like Dale Howard [MVP] or John - Project will share their possible workarounds for your scenario here based on their resourceful experience.
Please correct me if I made any misunderstanding or if there have anything else I can do for you.
Your patience is highly appreciated. Hope you a nice day and stay safe!
Best Regards,
Mia