To start, what belongs on the Physics Codidact is up to the people active on the Physics Codidact. The question seems to have been well received there, and I suspect that it would also have been well-received here.
Math questions of any sort are welcome here. However, when asking a question motivated from physics here, it should be asked in a way that it can be answered without physics knowledge. A question like "Does the canonical quantization of this theory have these properties?" would likely be off-topic here, because it assumes readers will know what canonical quantization is. On the other hand, a question like "Does this system of differential equations resulting from canonical quantization of this theory have these properties?" would likely be on-topic (depending on "these properties"), because it can be answered without knowing what canonical quantization is. The original question would probably be perfectly fine on the Physics Codidact.
Where a question is asked also communicates what types of answers are expected. Asked on Physics Codidact, many assumptions may be taken for granted and answers are likely to restrict themselves to physically relevant scenarios. Asked on Math Codidact, non-physical generalizations are likely to be considered which will lead to potentially different answers.