I was wondering around in my new 1.17 Pre-release 1 world and I noticed some bricks that looked like a Ruined portal so then I went into spectator and saw that it had generated underground. To my knowledge Ruined portals are not supposed to generate underground. Note this world was generated today (5/27/2021) in 1.17 Pre-release 1. Attached is a screenshot I took with the debug screen on. It also has the seed to the world.
MC-226507
World Generation for Ruined portal
Resolved
Invalid
0
Nope, this is working is intended per the 20w16a patch notes.
"RUINED PORTALS - Shattered remains of ancient nether portals. Wonder who built them? They can be found in any overworld or nether biome; some are hidden underground, under the sea, or buried in sand"