We only provide patches for version 126.96.36.199 of Magento 1. This is the latest version and any older versions won’t be supported. If you run a Magento 1 shop in an older version, but have always patched it, it is likely that our patches will work there, but we cannot guarantee this. We only test our patches for version 188.8.131.52.
We test all our patches under PHP versions 7.2, 7.3 and 7.4.
Older PHP versions like PHP 5.6 are not supported, because they are not supported by PHP itself.