Interesting. I just tested on a Pixel 2 XL running the latest public Android 11 OTA version and search doesn't lag at all. Same speed as on a iPhone 11 Pro Max.

Could it be a device issue? I highly recommend you report it to Bitwarden as Android can be a real pain in the ass to test with so many different devices out there with all kinds of strange OEM "optimisations" to the OS.