An experimental datapack to provide safeguards (and maybe auto-navigation in the future) for Elytra flight.
Suppress the automatic pitch-up functionality anywhere within an infinitely-tall cylinder of radius 25 blocks from ~ ~ ~ by summoning a marker entity as shown in the example below.
/summon minecraft:marker ~ 0 ~ {Tags: ["autopilot"], data: {autopilot: {suppressRange: 25}}}