I have a heavy sliding gate (around 350 kg) on wheels. I want to automate it. Gate moves 5 meters horizontally. Speed is not super important but it must be strong and reliable. Was thinking pneumatic because it’s fast but now I’m not sure. What type of actuator should I use for this? Any recommendations?

For a 350 kg sliding gate pneumatic might feel tempting but it’s actually not ideal – you need huge compressor, lots of air lines, and it’s hard to make smooth slow start/stop. Hydraulic is powerful but messy, expensive and overkill for home.
Best option is heavy-duty electric linear actuator. Look at industrial models with 3000–6000 N force. See the full explanation of actuator types here: https://www.progressiveautomations.c...ages/actuators
They have industrial electric actuators designed exactly for gates, barn doors, solar trackers etc. Usually 24V, high force, long stroke possible with track or standard style. Much cleaner and easier to maintain than fluid-based systems.

Track actuators are also good for gates because body length stays constant. But for 350 kg definitely check force calculator on their site first.