Koxiaet

You can get them to generate, but sometimes if you fiddle around with the settings they inexplicably won't; /locate will show a stronghold but going there will yield nothing.

Strongholds also don't generate on Superflat worlds - that needs to be added to the title.

This is a duplicate of MCPE-55339

FWIW I was able to produce a large region of overlapping strongholds near spawn with the following setup:

"structures": {
	"stronghold": {
		"distance": 0,
		"count": 128,
		"spread": 3
	},
	"structures": {
		"minecraft:stronghold": {
			"spacing": 2,
			"separation": 1,
			"salt": 0
		}
	}
}