Bash et al are great for command line use, but produce a situation of really bad engineering hygiene when used in scripts.
Do not use. Stay away. Bash et al considered harmful. Red flags on job interview when referenced.
Possibly the most important tip is to use ShellCheck (https://www.shellcheck.net/) as a linter on your scripts and work through the various warnings to eliminate them. For the rare times that ShellCheck is overly cautious, you can remove a specific warning with a comment before the offending line such as
# shellcheck disable=SC1091
Also, take time to look through Greg's Wiki as it is possibly the best Bash resource that discusses the various pitfalls: https://mywiki.wooledge.org/BashPitfallsAs a Bash script writer, I disagree with your "red flag" interpretation as that'll mean that you'll end up with poorly written Bash scripts along with a hotch-potch of different tools to achieve the functionality (e.g. different versions of Python required for older scripts and newer ones). Knowing Bash is also very useful for writing Dockerfiles.