Nice to have you here @Hasu
As long as both stETH and ETH have been granted borrowing power in normal mode (ie their LTV is not 0) they automatically gain the eMode boost when added to the category. Therefore if both have borrowing power, you will be able to use them both as collateral with 95% ltv
Of course this is just an example - the actual eMode parameters are configurable by the Aave governance, and depending on the underlying network and oracle speed, the ltv in eMode might be higher or lower
For example i feel like 95% ltv would be a bit risky for the protocol on ethereum L1, but likely fine on Arbitrum or zkSync with faster oracles and cheaper transaction costs