when attempting to change the Data type of an InnoDB table, from TEXT to JSON, given that they should be of the same storage format, we should not expect a table rebuild.
However, using both ALGORITHM=INSTANT & INPLACE fails. only works with ALGORITHM=COPY (which the implicit ALGORITHM=DEFAULT would map to in this case).
(P.S: Just a pointer to help, 10.4 already has fixed cases where changing the collation from utf8mb3 to utf8mb4 would not unnecessarily rebuild the table.)
will attach test scenario to show this.