alter.Schema().Add().Field("$.Nested.F1").Options("TEXT").Build() works as in the test case, however
alter.Schema().Add().Field("$.Nested.F1").Options("TEXT SORTABLE").Build() fails with Invalid field type for field '$.Nested.F1\'. error.

This is probably caused by the incorrect command definitions. The options should be marked as "multiple": true:

rueidis/hack/cmds/commands_search.json

{
"name": "options",
"type": "string"
}