Earlier quoted context omitted.
I've been using fish for nearly 10 years. First, there are some ways to make fish more compatible with bash. If you want to do some shell scripting in fish, or running other people's shell scripts (or commands) this may aid you since you wouldn't have to port them (or take less time to port them over). You can achieve this with a plugin system such as 'oh my fish' or 'fisher'. But, as always, it adds complexity (and…
./script.sh and script.sh just starts with #/bin/bash I'm simple
Shell scripts from third parties stick with whatever shell they were written for (ie. /bin/sh or /usr/bin/env bash), and commands copy/pasted from the internet are either quickly executed with bash (one-off) or ported over. Because I like to have such in my history (fish is configured to use atuin), I want to keep using the same shell, so I try to stick with fish. If I cannot convert a command (usually a bunch of commands) to fish, it is PEBCAK and a learning curve/experience.
As for tmux, that is solid advice, because it also allows to stick with a shell which is known to work. I've come to like zellij with alacritty, with zellij the option is default_shell. But now that I use ghostty, I don't use a terminal multiplexer locally any more; only remotely. And there I still use tmux.