$b="\N{U+007B}"

Note that's a double-quoted string, and you don't need to escape {'s there - unless of course you mean using that escape in a regex, and while /\N{U+007B}/ certainly works, it's a whole lot longer than the equivalent /\{/...

Are you suggesting that a person sandbox the application and boil the perl version up?

Yes, that's exactly the suggestion (though "test environment" would be more accurate than "sandbox"). It's of course a bit of work and may seem like overkill; many people do end up not doing this and jumping several years into the future like in this case. But when that then leads to problems (like in this case), one way to debug is to gradually step up the Perl versions so one catches all the deprecation warnings before they become fatal errors or confusing syntax errors.