Go to see perl. Scroll down to the History section. Looks at the Incompatible Changes section of the perldelta documents for .0 versions.

• Perl 5.18's incompatible changes
• Perl 5.20's incompatible changes
• Perl 5.22's incompatible changes
• Perl 5.24's incompatible changes
• Perl 5.26's incompatible changes
• Perl 5.28's incompatible changes
• Perl 5.30's incompatible changes
• Perl 5.32's incompatible changes
• Perl 5.34 has no incompatible changes
• Perl 5.36's incompatible changes
• Perl 5.38's incompatible changes
• Perl 5.40's incompatible changes