Trojan.MacOS.Miner is a generic detection probably triggered by a trojan with crypto mining capabilities. While the prices of cryptocurrencies are volatile, cybercriminals will likely continue to deploy miners as they can be a lucrative revenue stream.
Trojan is a name derived from ancient Greek mythology. As the name suggests, this type of threat usually presents as something else. The most common way for trojans to infiltrate a system is to be included in freeware bundles or cracks for paid software. Users are advised to try to avoid installing bundles. If they decide to do so anyway, it is very important to check the "custom" or "advanced" setup options and remove any component they don't want to install.
Once a trojan infiltrates a system it may serve many different purposes. Miner trojans usually try to abuse the infected system's resources to generate cryptocurrency. Crypto mining is most often done through the CPU and sometimes the GPU of a computer. This can result in some noticeable symptoms like performance deterioration as mining can be a very resource-heavy process. To avoid detection certain miner trojans monitor the system's resources and only mine when the system seems to be idle.
Whatever the particular trojan miner is, the user should try to remove it. The easiest and most efficient way to do that is to use an anti-malware solution. Since a miner trojan's success is very much dependent on it staying hidden, it's unlikely that it would download additional more severe threats. Nevertheless, it is highly recommended that users remove such threats, unless they are adamant they want cybercriminals to profit off of the user's hardware resources.