The /data command now supports a string type with /data modify storage <name> <target> set string, but the /execute store result storage doesn't support string types.
Comments 3
It appears quite strange to me, that besides the data command, no other commands support the new string feature, making it impossible to further process the data. Maybe at least the behaviour of /data modify storage <target> <targetPath> modify string storage <target> <targetPath> should be adjusted to flatten the json aka "interpret it" (like the /tellraw does) into a string, instead of throwing an error?
execute store stores either success count, or resultcommand result, both of which are always integers. /data get result for objects, lists/arrays and strings are the tag count, list/array length and string length.
This is a feature request and not a bug.