Diagnosis
You've got weak signal strength, almost always due to a dying remote battery or interference from the opener's own light bulb.
How to Fix It
Start with the simplest fix. 1) Replace the battery in your remote (it takes a 12V battery, type 23A). 2) While you're at it, unscrew the opener's light bulb. Try the remote. If it works consistently with the bulb out, you've found the issue. 3) The old incandescent bulb can cause radio frequency interference. Swap it for a modern LED bulb, which won't cause this problem.
If That Didn't Work
The antenna wire on the opener might be damaged, shorted, or tucked away. It's a thin, coated wire hanging from the back of the motor unit. Make sure it's fully extended and not touching any metal or bundled up.
Heads Up
Don't use "smart" or "dimmable" LED bulbs in the opener. A basic, non-dimmable LED is what you want. The electronics in fancy bulbs can sometimes create their own interference.