i was also having said problem i wasnt sure which mod it was from, but if you end up finding a strawberry you should be able to use an iguanadon to turn it into a seed and then plant it(unless my strawberry items were indeed from a different mod)

I found some seeds on the Lost Island but they're very rare

the prehistoric beasts mod interferes with harvesting strawberry seeds so delete it and gather the seeds from bushes and then you can reinstall the mod when you have enough strawberry seeds