Capsuleando is a creative slang term you won't find in a standard dictionary, likely invented by the artist. It's formed from the noun cápsula (capsule) and the gerund ending -ando.
In the song, Mora sings, "En la Mercedes voy capsuleando," which describes the feeling of driving his Mercedes as if he's in a private capsule, zoned out and disconnected from the world around him. It perfectly captures a modern vibe of cruising while being lost in your own thoughts and feelings.
Mora is completely stuck on someone in this song, and he's not trying to hide it. He lays out his frustration from the very beginning, admitting he enjoys seeing this person even if they aren't together anymore. He's totally obsessed, telling her, "Mis letras siempre tienen tu nombre y apellido" (My lyrics always have your first and last name). He can't move on, even though he knows he should. He uses a great Puerto Rican phrase, "Más alante vive gente, pero no me he movido" (Life goes on, but I haven't moved), to show just how stuck he is in her memory.
The whole song builds to a simple, very direct point. Despite all his frustration and his attempts to forget her, he's completely at her mercy. If she calls, he's dropping everything. The chorus is a promise: "si me llamas, le llego volando" (if you call me, I'll get there flying). He'll speed over in his Mercedes, ready to pick up exactly where they left off. It's a classic reggaeton theme of being unable to resist a toxic attraction, driven by intense physical chemistry and memories he can't shake.