Some notes:

1. The ".env" file should have an "LF" end-of-line sequence.
2. Avoid using dynamic values in environment variables, such as variable1=$variable2@$variable3
3. Avoid using a quotation (") in environment variables vavlue, such as variable="value"

This is the best and shortest answer

source .env && export $(cut -d= -f1 < .env)