As someone who got sick of old school PHP and server-side rendering, mobile development, AngularJS/Angular/TypeScript madness, backend development, pure database development and what not I can tell you one thing: Everything is in our head and it's all because of the fear of staying behind. Once you start listening to yourself and once you start focusing on solving the problems as simple as possible, you will be happy in doing any kind of work. It's OK to be aware of new technologies, but you should use only those that make you happy and that actually solve the problem in a simple way. Why should I feel guilty if I'm not using some technology? Keep in mind that many technologies, frameworks are just products and the main reason behind the hype is money. Focus on general topics like software architecture, clean code, algorithms, best practices, database design skills and make sure to isolate yourself from hype.
I would suggest you not to choose Blazor. It's not that Blazor is bad or that I have something against, but you don't want to limit yourself when it comes to finding a Blazor developer. You will hardly find a frontend developer who is focusing on Blazor.
Today are React, Angular, Vue or similar frameworks the best way to go, especially for a startup where you need flexibility. Keep using .NET for a backend, provide a nice API and implement frontend using already mentioned frameworks.
Great idea :) My only question is how the authentication works there...? User has to be logged in on the worker phone's app in order to do something on Instagram. I mean, I don't think anyone shares his Instagram password with an 3rd party software. Or you provide the services which can be done from another(your) Instagram account - which is then signed in on all worker phones?