Not that is public. But, hypothetically if a large agency that issues M models tested Gen 5 G26s because there is no 26M, they might find the M models triggers broke in and stayed nice while some 26.5 triggers degraded but the guns still worked.
My understanding is the coating on M internals is simply DLC. Several other federal agencies are buying Glock 17/19 Ms off the FBI contract including the DEA, US Marshals, State Dept DSS, and, I believe BATFE so there is a fair demand for them.