If you have a typical .env file consisting of bash style variable assignments:
SITE="Salt Amphora"
URL="http://example.com"
AUTHOR="John Doe"
The following one-liner can be used to load all of the entries as environment variables in Nushell:
grep -v '^\s*$\|^\s*#' .env | lines | split column "=" k v | each {|x| {$x.k: $x.v}} | into record | load-env
Equivalent for bash:
export $(grep -v '^#' .env | xargs)