As in the title, the generated biome is too small. To prevent chance, I tested the cherry grove area of the latest version of biomebackport in three different new saves, and the results are shown in the first three images below. Obviously this is a problem, because the cherry grove biome in 1.20 must have large generation, as in the last picture (which is 1.20).
Suggestions for a solution: 1. Increase the generation area 2. Configurable generation size in the config file.