(archived for 5.1): Check XDA or LineageOS wiki (MindTheGapps-5.1.1)
Note: The date will be old (e.g., 2020 or 2021), but that’s fine—older Gapps for 5.1 are more stable. gapps android 5.1
If you already booted into Android 5.1 without Gapps: (archived for 5
While their homepage defaults to the latest Android version, they maintain an archive of older releases. However, navigating these archives can be tricky. 2020 or 2021)