If you loved Godzilla: Planet of the Monsters, try Godzilla: City on the Edge of Battle
A bridge between a film you've already seen and one most people haven't. Here's what they share, and what the second one does that the first one doesn't.
You already loved

Godzilla: Planet of the Monsters
→
Try this next

Godzilla: City on the Edge of Battle
What they share
Both films are directed by Hiroyuki Seshita, Kobun Shizuno, and they both carry the dread mood tag, and they sit in Animation / Science Fiction territory. If that's the register that drew you to Godzilla: Planet of the Monsters, the second film will land in a comparable space — through a different lens.
dread
What Godzilla: City on the Edge of Battle is
Halo without Master Chief. After twenty millennia, humankind returns to a Godzilla-dominated Earth, seeking a weapon lost to time: Mechagodzilla. This animated installment delivers kaiju action and existential pondering in equal measure.