Nothing stands above the supreme. The word is the superlative form of Latin super — 'over, above' — taken to its absolute limit. Latin suprēmus meant 'the very highest', and English borrowed it in the 16th century with that meaning intact.
The Proto-Indo-European root *upér, meaning 'over', branched into dozens of English words. Through Latin super came superior, superlative, superb, and soprano (the highest singing voice). Through Old French came sovereign — the one who governs from above.
The German branch preserved the root as über, meaning 'over' or 'above'. English borrowed über directly in the 20th century, giving us words like übermensch and the casual prefix uber- meaning 'extreme'.
Supreme entered English not through the usual Old French pathway but directly from Latin, likely through legal and theological texts. The Supreme Being. The Supreme Court. In both cases the word carries its original force: the highest authority, beyond which there is no appeal.
In French cuisine, a suprême is the finest cut of poultry — the breast removed whole from the bone. Even in the kitchen, supreme means the best and highest.