An example set of unique seeds that have the same structure seed:

• 1537979277936836042
• 2296272865195343306
• 2329486912447200714
• 2135269178516848074
• 2561140818280070602
• 2597169615299034570
• 2626443012876942794
• 2734247928957124042
• 3391773474553216458
• 3482408417054047690

How to Reproduce: Notice that, besides the placement of structures, several world generation aspects are identical across these seeds no matter where you go in the world, as long as the same coordinates are compared

• Nether Biomes, down to the exact block and not just the 4x4 (need to do more research on this)
• The shape of Nether Fortresses, block for block (I assume this is not intended, as the same behavior does not exist for other structures such as Bastion Remnants and Strongholds. Chest Loot is still unique for each seed)
• End Biomes, down to the exact block and not just the 4x4
• The shape of End Cities, block for block (I assume this is not intended, as the same behavior does not exist for other structures such as Bastion Remnants and Strongholds. Chest Loot is still unique for each seed)
• The exact terrain of the end, block for block, in the entire dimension (excluding End Gateways, Chorus Fruit, and small End Island placements)

Can confirm for worlds down to 1.18.