Since you cannot jump directly from High Sierra to newer macOS versions like Ventura or Sonoma (due to hardware limitations on many 2012–2014 Macs), Catalina is often the final supported version for older machines. Importantly, , making the upgrade critical for safe internet use.
If possible, partition your drive (40GB) and install Catalina fresh while keeping High Sierra for fallback. how to update macos high sierra 10.13.6 to 10.15
Below is a detailed, safe walkthrough to get you from 10.13.6 to 10.15. Before doing anything, confirm your Mac can run Catalina. Since you cannot jump directly from High Sierra