Is this because of some hardware issues or because R4.x hasn't been released yet? Would it make sense to wait for R4.x before purchasing?
Optimistically speaking, a truly open hardware ecosystem (i.e. Risc-V, OpenPower) will likely take ~3-10 years to become commercially viable. Considering the pragmatic approach that Qubes OS is taking, it would seem ideal to get the most secure and privacy-protecting hardware in the short-term until such time that we can have "truly" secure and privacy-protecting hardware in the long-term.
As Marek pointed out, the Librem 13 would work with Qubes OS 4.x and "may be somehow more secure with Coreboot (less places to hide some backdoor), but may be also less stable - depending how mature is Librem 13 support in Coreboot." As Grzesiek pointed out, waiting until 4.x to be released makes sense since "a better option might present itself". In addition, it would give Purism an opportunity to right a wrong.
That said, besides the Librem 13, I haven't seen nor heard of another laptop that provides hardware switches to disable camera/audio/wifi and components that do not require blobs (CPU excepted of course). Besides my Google Pixel LS Chromebook running linux, I'm unsure whether there is a better option at this point.
Thanks,
Roberto