For Go, I just picked up Fyne. Deploys natively on all relevant targets, with a consistent UI across platforms.

No accessibility.

Great multiplatform UI framework doesn't exists currently. Next best thing is to choose a framework that best fits your requirements.

True enough, but is there something less-great? Or not-so-bad?

What are the requirements?

Single or multiplatform? Which OS?

Will there also be a mobile or web version of an app? Or embedded?

How well does it need to integrate with target platform? How native it must feel? Does it access to native platform features?

Does it need to be lightweight?

Does it need very low latency? Is performance critical?

Does it need many custom widgets or none?

Does it need to have quality implementation of any specific widgets available (like charts, maps etc.)? Big widgets ecosystem?

Does it need heavy widget trees?

Does UI need to be customizable by users?

How important is accessibility?

Programming language preferences and limitations?

How important is developer productivity?

Can framework be proprietary or non-free?

Is it maybe just to learn UI development?

We do web-only right now. No frameworks. Maybe focus on MDN if you think you can get the business done with a webapp. Once you master flex, grid & friends, you will be set free.

If we are still insisting upon native apps, I am growing increasingly-curious as to what the reason could possibly be. Unreal & Unity deploy to the browser. What does your business do that is so special by comparison?

HTML is a bad replacement for a proper UI toolkit, that's the appeal. There are so many problems that good UI toolkits and languages solve that HTML just ignores and always will. But, Chrome gets a massive budget, web apps are easy to deploy thanks to the ubiquity of browsers, and there's safety in numbers, so those things usually outweigh the other concerns. Doesn't change the fact that there is plenty of scope to compete with HTML.

Check flutter.

For .NET specifically, you would need to reach for 3rd party frameworks. Avalonia in particular is excellent.

WPF is probably your best bet for desktop UI if you want to stay in the MS ecosystem.

Give Uno Platform a try https://github.com/unoplatform/uno