1.21.50 introduced a data driven jigsaw structure experiment to use jigsaw blocks in behavior packs, and microsoft docs updated to reflect this, but there seems to be an issue with either the documentation or the game.

For the worldgen processors the docs say there is a  "predicate_type": "minecraft:archeology_block_loot" but when trying to use this (even with a direct copy paste of the example provided with just a different identifier) the game throws these errors:
[Structure][error]-Loading Jigsaw Structure .json files | Jigsaw Structure Processor List .json file worldgen/processors/sus_placement.json |  -> predicate_type: This value is bound to 'PositionalBlockRuleAxis' and expects one of the following strings: 'minecraft:always_true', 'minecraft:axis_aligned_linear_pos'. Found: 'minecraft:archeology_block_loot'
 
[Structure][error]-Loading Jigsaw Structure .json files | Jigsaw Structure Processor List .json file worldgen/processors/sus_placement.json |  -> processor_type: wrong const value for member "processor_type"
 
 
I looked in the game files for the example they provided with the minecraft:trail_ruins_roads_archaeology file and it instead uses "predicate_type": "minecraft:block_match" with this instead:
 
"block_entity_modifier": { type: minecraft:append_loot",
..

Microsoft Addon Docs:
https://learn.microsoft.com/en-us/minecraft/creator/reference/content/worldgenreference/examples/jigsawprocessors?view=minecraft-bedrock-stable

Steps the reproduce:

1. Create a jigsaw structure behavior pack that uses "predicate_type": "minecraft:archeology_block_loot" as stated by the docs
2. Turn on the creator log UI and file in the game settings
3. Create and start a world with the data driven jigsaw structure experiment and behavior pack enabled 
4. Check the creator log and see the errors the log throws out because "predicate_type": "minecraft:archeology_block_loot" doesn't exist