I appreciate your effort in keeping this thread updated about the progress of your concern, @Sggrooming.

You're correct that we have received reports about the unavailability of the QuickBooks Mobile App to populate sales taxes on estimates and invoices. With that, I'd like to encourage everyone experiencing the same to contact our Technical Support Team to add them to the list of users reporting the same concern. For now, we can follow the workaround suggested by the support you spoke with to add sales taxes by logging into your mobile or web browsers.

Moreover, you can go over to this article to learn about recording, adjusting, and deleting sales tax payments in QuickBooks: Manage sales tax payments in QuickBooks Online.

I'll keep this thread open for everyone to share and post their queries. The Community is available 24/7 to help. Take care!