Is systems a plural possessive

No, the Word systems is the plural form of the singular noun system.

A possessive noun is indicated by an apostrophe.

A plural noun that already ends with an s simply adds an apostrophe after the s at the end of the Word: systems'

A singular possessive noun is formed by adding an apostrophe s to the end of the Word: system's

Examples:

The systems that need repair are posted on the log. (plural)

The systems' problems are also listed. (plural possessive)

A system's repair is noted by the mechanic. (singular possessive)