No, yaySIM does not provide an unlimited data eSIM for Montenegro. All of the plans listed for Montenegro have a hard data cap of 20GB.
Travelers who need a larger data allowance can choose from fixed data plans that offer 20GB for a set period. For example, the ME_20_30 plan gives 20GB for 30 days at $33.36 USD, and the GL-139_20_90 plan offers 20GB for 90 days at $92.48 USD. These fixed data plans can be more cost‑effective for most users unless they are extremely heavy data consumers.