If you have AC-powered Opensprinkler, you can get 24VAC relays. These are not the most common type of relays, but they are available at digikey.com or mouser.com if you search for 24VAC relays. You likely need to do soldering as these relays come with pins/legs but not screw terminals. You can also use pump start relays, as they are essentially 24VAC relays but primarily used for switching pumps and are quite bulky. I’ve previously written an article about the various options for 24VAC relay:
https://opensprinkler.com/using-24v-ac-relays-with-opensprinkler/
If you have DC-powered OpenSprinkler, you can use solid state relays. These are widely available, and they come with screw terminals so no soldering required. For example:
https://www.amazon.com/SSR-40DA-Single-24-380V-Temperature-Controller/dp/B09NPPLDDT
If you would rather not mess with high voltages and power-line wires, the safest option would be to get an RFToy and RF remote power sockets, then you can use OpenSprinkler to wirelessly toggle power sockest:
https://opensprinkler.com/product/rftoy/