The bug
Since 20w21a, strongholds don't generate in Bamboo Jungles and Bamboo Jungle Hills in the Overworld. This only affect "normal" worlds, strongholds still generate in single-biome worlds or worlds with other custom biome generation.
An affected stronghold can be found in seed 14916203336864, at coordinates [-10000, 4384] (see attached screens). Notice that the stronghold is present in 20w20b, but has moved ~80 blocks in later versions so that the starting point isn't in a Bamboo Jungle biome anymore.
This is probably caused by the POSSIBLE_BIOMES list in OverworldBiomeSource missing the Bamboo Jungle (Hills) biomes.
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I'm also unable to reproduce in a single biome world - strongholds do spawn in Bamboo Jungles. Though someone else has claimed the code portion of this (MC-188821), so the issue may be that the `POSSIBLE_BIOMES` list in `OverworldBiomeSource` is irrelevant code.
I'm pretty sure strongholds DO NOT generate in Bamboo Jungle in worlds with normal biome generation. See the added screenshot; even if the stronghold extends into the neighboring Bamboo Jungle, the starting point isn't in a Bamboo Jungle but in a Modified Jungle biome.
Note that once a Bamboo Jungle stronghold changes position, this affects every other stronghold after it, which means that other unrelated strongholds will also change position: this is what caused structures to "move in the world".
Finally, the fact that strongholds generate in single-biome worlds actually gives evidence to my theory: the single-biome BiomeSource will properly report its available biome list, unlike the default OverworldBiomeSource.
I think they still can spawn in bamboo jungles, because the stronghold location generator falls back to some "biome search starting point" if no suitable biome is found within a certain range. So if that starting point was a bamboo jungle, and no suitable biome is in the area, it would spawn there.
But it's probably far less likely now.
This report is invalid. They still generate is Bamboo Jungles. Structures where changed in 1.16 causing them to move in the world.