I just installed e-2.1-t-20240605406922-dev-sunfish.zip to a 4a that had Android 13 stock ROM on it.
Following the instructions as linked above in combination with [HOWTO] an Unified Install Guide Project for /e/ worked very well for me - I completely followed the instructions along and also did the dtbo- and recovery- steps before actually flashing eOS…
Pretty straightforward and fast execution once I had understood that I had to copy the downloadad files into the same folder as adb…or:
… respectively 
And that would be my only suggestion: to clarify that “where to download the files for availability in adb and fastboot”-thing in the guide as it was just unclear for me as an adb-and-fastboot-newby (or maybe I have just overread it?)
Else: pretty cool! 
Thanks a lot for the guidance!!!
Edit: for the official pixel 4a-guide (and presumably others as well) it would be helpful
- to inform the user about the recurring "bootloader is unlocked … " -warning that occurs at every boot once eOS is installed on the device
- to give clarification on whether and why relocking or not relocking the bootloader is advised …