Key with dot notation in rank features of ES v8.4.0

[Chen_Bright]

ENV: Elasticsearch v8.4.0
operation steps(very simple):

what i wanna know is, how can i insert this kind of data in the rank features field?(i tested in es v7.10.2, it works, so maybe es changed the way to treat the key field in the new version?)
sry i am not so familiar with 'rank_features', so if u have any ideas, can share with me? thx a lot!

[Chen_Bright]

when i tested in es v7.10.2, it turned out to be:

[Chen_Bright]

Problem probably solved...
adding '"subobjects": false'(which starts in es v8.3 and didn't mentioned in release notes) in mapping can disable object support in the entire index
but it only works on 'rank_features' not 'rank_feature', that is weird...