Is Pop/Rock a catchall genre for both Pop and Rock music?

Great question. Short answer: Yes.

AllMusic has a group of 21 overarching Genres which are sort of generic buckets of categorizations of music. Jazz, Country, Rap, Classical, etc.

Pop/Rock is one of those broad categories that can encapsulate anything from Elvis to Metallica to Britney Spears to the White Stripes to Lady Gaga.

Within those Genres, we also have more specific Styles that better break down the type of music itself (within the umbrella of Pop/Rock).

From our Pop/Rock page: https://www.allmusic.com/genre/pop-rock-ma0000002613

Rock & Roll is often used as a generic term, but its sound is rarely predictable. From the outset, when the early rockers merged country and blues, rock has been defined by its energy, rebellion and catchy hooks, but as the genre aged, it began to shed those very characteristics, placing equal emphasis on craftmanship and pushing the boundaries of the music. As a result, everything from Chuck Berry's pounding, three-chord rockers and the sweet harmonies of the Beatles to the jarring, atonal white noise of Sonic Youth has been categorized as "rock." That's accurate -- rock & roll had a specific sound and image for only a handful of years. For most of its life, rock has been fragmented, spinning off new styles and variations every few years, from Brill Building Pop and heavy metal to dance-pop and grunge. And that's only natural for a genre that began its life as a fusion of styles.

Near the bottom of that page is a breakdown of the individual Styles within Pop/Rock:

Pop is a style under the pop/rock genre.