From the /e/OS page Different Build Types this is the definition of Unofficial builds.
- Builds are made by /e/OS or external users
- Builds are not supported by /e/OS
- Made using /e/OS sources code with no modifications in any form
- At times may not have a maintainer as in made by a user who does not own the device
- Do not receive OTA updates
- Available for download on /e/OS websites and are tagged as “UNOFFICIAL”
- Release Frequency: Monthly or biMonthly
- Build Naming format: e-0.7-n-2020021341116-UNOFFICIAL-mata.zip
- Install these builds at your own risk
I suggest before install to read the description of the Lineage (unofficial) build the sources of which are used. Same thread as above
Alternatively if waiting for the official OTA upgrade path note also the comment