Isn't "Thiel Truth" just a euphemism for a strongly-held opinion? Not sure why this banal concept has to be attributed to some venture capitalist. Seems like clickbait.

That aside, just use whatever fits best for the task at hand. If server-side rendering works better for you, use that. If client-side rendering is preferable, do that instead. Or a mix of the two. No need to be dogmatic about it.