Dear Amanda Wilkinson,
Good day!!
I understand your concern but as per official Microsoft KB, currently there is no any particular application replacing the Publisher app but Microsoft is exploring the modern ways to achieve common Publisher scenarios and they will release the detailed blog when there is any update.

Moreover, I suggest you add your valuable feedback in the Publisher application (Open the Publisher app> Feedback at the bottom left> Send a Suggestion) which is the best place to share our ideas and improve the Microsoft products.
In addition, I will keep this thread open so that MVPs and experts in this community can share their ideas on this scenario.
Appreciate your patience and understanding. Have a great day!!
Best Regards,
Sophia
Dear Microsoft Team / Sophia,
I must express our deep frustration regarding the current situation with Microsoft Publisher. Our company has relied on Publisher for over 25 years, accumulating over 7,000 files that would be nearly impossible to redesign or import into any other Microsoft product without have to do major revisions.
This is completely unacceptable. We urgently need a response outlining our real options moving forward. At the very least, these Publisher files should allow for straightforward conversion to Word (keeping all styles, formats etc... in tack without needing to redo the whole project), which is the alternative being suggested to us.
It’s extremely unprofessional for a software company of your stature to leave users in this predicament. We urge you to reconsider your approach—either by maintaining the product or ensuring that users can seamlessly continue using it with Microsoft 365.
We look forward to your prompt response.