Suppose we got nuked or some calamity caused the interruption of all the fancy x-nanoneter processes. What would we actually miss out on? I don't know what the latest process nodes we have stateside are, but let's say we could produce 2005 era cpus here. What would we actually miss out on? I don't think it would affect anything important. You could do everything we do today, just slower. I think the real advancement is in software, programming languages, and libraries.
I used to daily-drive a Thinkpad X200 from 2008. As soon as you touch the modern (i.e. bloated) web, you feel the slowness. Other than that and gaming, it ran fine.
I'm talking about way more than just CPUs... And for your question, we'd pretty much miss out on modern-like mobile phones entirely. 90nm -> 18A/1.8nm is a LOT of reduction in size and energy... not to count the evolution in battery and display technology over the same period.
Now apply that to weapons systems in conflict against an enemy that DOES have modern production that you (no longer) have... it's a recipe for disaster/enslavement/death.
China, though largely hamstrung, is already well ahead of your hypothetical 2005 tech breakpoint.
Beyond all this, it's not even a matter of just slower, it's a matter of even practical... You couldn't viably create a lot of websites that actually exist on 2005 era technology. The performance memory overhead just weren't there yet. Not that a lot of things weren't possible... I remember Windows 2000 pretty fondly, and you could do a LOT if you had 4-8x what most people were buying in RAM.
I have an unpopular pet theory: the exponentially growing software bloat actually exists to slow computers back down to bearable levels for common folks, and that's why the most bloated frameworks have consistently replaced obsolete, less bloated ones, throughout the last decade.
Why else are everything now seem to be wrappers for wrappers? What if the bloat was, subconsciously or whatever, the point?
One superpower being in 2005 for CPUs and another being in 2030, and at cold/hot war, would be decisive.
If society as a whole reverted to 2005, we would be fine.
Software is much, much more bloated today than it was in 2005. 64-bit CPUs were available, but not quite mainstream yet. A "high end" consumer system had a couple gigabytes of RAM and chipset limitations generally capped you out at 4 or 8 gigs. You were lucky to have two CPU cores.
If you took today's software and tried running it on a memory constrained, slow, 2005 era system, you'd be in for some pain.