You asked for codes, its hard to see but one violation I often saw in my inspection days was no attachment to the floor (2018 IPC 405.4.1, 405.4.2) As far as the level, that would depend on the MFR instructions. Some have a requirement, some don't. Oatey, for example says "flush with or on top of the finished floor". Never have I seen an installation lower than than the level on which the toilet will rest that made me comfortable, but small tolerances can be absorbed by the use of the various products designed to accommodate them. Your picture would definitely prompt me to ask them for the MFR installation instructions. Which, of course, would be hard to come up with. In that case I would revert to the industry practice of level or on top the finish floor.
How do we cite that? 2018 IPC 102.9 "Any requirements necessary for the strength. stability or proper operation of an existing or proposed plumbing system,.....not specifically covered by this code shall be determined by the code official". The condition you show would definitely be considered "operation".