It is possible to deliver a lite, PWA/SPA with vanilla JS and no loading spinners. Users can install it on their mobile device. I've done as much with blockchain dApp front ends. It isn't necessary to hijack the address bar or abuse the back button to achieve this. Modal dialogs, collapsible elements, tabs and simple anchor elements are enough. Yes, you can allow in-app back buttons to return to the previous modal's state, although that might suggest that the UI pattern should be simplified.

"State management" from a framework seems ridiculous. Developers should be able to handle their application's state with JSON objects representing reasonable abstractions of concerns. Typically, this would be similar to the data you query from the web. Therefore, upon launch, you can populate your document using <template> elements from cached data in localStorage or some of the newer options. When network connectivity is available, you can update the state using the same functions.

Perhaps this isn't something you would trust your large enterprisey team to do competently, but for a solo developer with a distaste for React and heavy frameworks, it seems like the obvious approach.

Interested to hear how others building sans frontend frameworks. If you love React and loading spinners by all means feel free to ignore this. To each their own.