There is a command to list the content of the payload file,
./payload-dumper-go -l e-2.6.3-u-20241217455391-community-river.zip
(thanks to @aibd) [Walkthrough] Extract eRecovery and boot images using payload-dumper-go
And another command to extract the wanted boot.img file
./payload-dumper-go -o OutputFolder -p boot e-2.6.3-u-20241217455391-community-river.zip