alex_g_offline is a spotify archive of Various Alex G recordings.

Many people speculate whether it is official or not, however if you look at the publishing records for the albums, you can find that it is linked to "DOMINO US PUBLISHING COMPANY", which has also distributed many Alex G songs on his main spotify profile.
You can check it out yourself here: https://credits.muso.ai/profile/ce883b3a-bfe5-46c4-9c32-06782095e049/credits

If you still have suspicions, you can go to https://unreleasedalexg.com and put the tracks as local files on Spotify or Apple Music. Read more on Last.fm. User-contributed text is available under the Creative Commons By-SA License; additional terms may apply.