To be honest, I've never heard of Bash's @Q solution before today--I can't find it in https://tldp.org/LDP/abs/html/, which is my usual goto guide for "how do I do $ADVANCED_FEATURE in bash?"
To be fair that's missing a lot. I'm not sure how much is just showing its age and how much it never had. The actual bash manual is quite informative.
In particular, failure to mention `printf -v` is horrible. Not only is it better performing than creating a whole process for command substitution, it also avoids the nasty newline problem.
`printf -v` was added in Bash 3.1 (2005). I think revisions of ABS predates that; but ABS has certainly been updated since then (last in 2014), and has no excuse for not including it.