Output exa results differently in scripting environment with grid options

If exa does something unexpected, or its output looks wrong, or it displays an error on the screen, or if it outright crashes, then please include the following information in your report:

• The version of exa being used (exa --version)
• The command-line arguments you are using
• Your operating system and hardware platform

If it’s a crash, please include the full text of the crash that gets printed to the screen. If you’re seeing unexpected behaviour, a screenshot of the issue will help a lot.

• exa --version: v0.10.1
• System: OS: macOS 12.0.1 CPU: (12) x64 Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz Memory: 24.61 MB / 16.00 GB Shell: 5.8 - /bin/zsh

In scripting environment. I hope to be able to record the output of exa completely, but as you can see, it is output in oneline form, but I have specified my options --grid but it doesn't seem to take effect.

Reproduce:

a="$(exa --color=always --grid)"
printf "%s\n" "$a"

printf "%s\n" ""

exa --color=always --grid

Guess: whether with [ -t 1 ] is forced output processing