> instead of
<= instead of
>= instead of
== instead of
!= instead of
if (( 2 -lt 3 )) then echo "True" fi
if (( 2 < 3 )) then echo "True" fi
-eq and friends are flags for the
test command aka
[. You are instead using it in an arithmetic context, such as
(( .. )) or
$(( .. )), where you should be using
== etc instead.
In arithmetic contexts,
-lt is simply interpreted as "subtract the value of
$lt", which is clearly not the intention.
If you do want to subtract
$lt you can add a space to make this clear to ShellCheck:
echo $((3 - lt))
ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.