It's complicated, and basically comes down to Vitalik's observation that "Ethereum is a currency in service of a protocol, while Bitcoin is a protocol in service of a currency." Basically the Ethereum devs set the economics to incentivize the correct behavior from players in the ecosystem, and this can be either inflationary or deflationary depending on gas prices, network usage, amount staked, etc. It's responding to the supply & demand for computation on the network.

For most of its history Ethereum was inflationary. It flipped and became deflationary a couple months back, and not coincidentally the price started rising again. It's likely to be significantly deflationary under Eth 2.0 with expected transaction and staking volumes.