Looks like if you have the following:
pahole is not installedthen the system may not boot.
The solution seems to be installing pahole. That should be done now, before updating to linux 5.11.
Is it ok if I pin this to the top of this section for better visibility?
What the hell is pahole?
It seems to be an issue with kernel 5.11 and dkms in general, not just nvidia. I ran into issues with acpi_call and bbswitch modules as well.
Short summary here … it’s build utility of sorts …
pahole
edit …it’s also a core archlinux package
This is required for building against the Linux kernel - upstream are discussing adding it as a dependency of the linux-headers package.
* for people running [testing]. It’s always worth specifying where the issue is happening. 
Better safe than sorry! 
Of course this is in testing, but remains to be seen what the upstream does.
Alternatively one can install the LTS kernel too, then there’s a simple way to boot and fix stuff.
Many ways to go forward.
Sorry … I’ve honestly had so few issues over time I forgot I was even on testing!
Very, very true. I was once told that testing was mostly a “no-drama zone” and I didn’t believe them. I stand corrected. 
Join the Arch testing team and start signing off packages as working.
We should have a category pre-warnings (hope this term is OK also to native English speakers ). But feel free to add a better term.
Maybe just prefix thread with [Testing] ?
Then maybe people start thinking this is not for me…
Would it matter if you are on “non-arch-way” installed system?
Are you running Arch-only base packages (e.g. no mesa-git packages)? Are you confident that you know your system inside-and-out in the same way you would if you installed following the Installation guide?
If yes to both, go for it.
On the other hand, if you’re running some weird combination with unofficial user repositories and don’t know what packages are influencing what behaviour (or are running a heavily customised derivative like Garuda) then no, don’t do it.
Yes to the first question.
I guess so to the second 
pre-warnings seems odd since they aren’t really pre-warnings but real warnings about potential future issues.
How about something along the lines of “Notices of upcoming changes”?
A “Testing” subcategory perhaps?
Some of the things aren’t related to testing specifically but are general things to be aware of which haven’t arrived yet.