How could I modify

RedirectMatch ^/?folder/(.*) https://elsewhere.com/abc.php?var=1\&d=$1

to include the best, to ensure that when the address is folder/printer then it doesn't redirect, but anything else does?

RewriteEngine On
RewriteRule !^/?folder/printer/

above (!) your RedirectMatch should have the desired effect.

Also, take a look at this post