after 2 hr of playing I notice massive fps drops in some part of the house (and they aren't same spot in each chapters) and during conversation/scenes although idk if it's because the game or my device itself (it's pretty old roughly 7 years now)

device

HP 15-db1000AX

 (AMD Ryzen 3 3200U with Radeon Vega Mobile Gfx  2.60 GHz , 4 GB ram)

The base game, Coffee Story, has over 100 4096x4096 texture pages, which take up about 6gb of VRAM when fully loaded. And while I tried to cut down on unused assets for this game as much as possible, a lot of them are just too integrated to remove. I believe it goes up to 5GB. I imagine what’s happening is as you play, more resources get loaded in, eventually capping your VRAM and then sprites get loaded into your RAM instead, impacting performance.

tl;dr You’ve just about got the minimum requirements to run this covered.