Ethernet plug RJ45 and RJ11 has different standards, different sizes (RJ11 has 6P6C\6P4C\4P4C\4P2C), where C stands for the number of pins of the crystal head; RJ45 has 8P8C).
Ethernet plug RJ45 and RJ11 are of different sizes (4 or 6 pins for RJ11 and 8 pins for RJ45), it is obvious that the RJ45 plug cannot be inserted into the RJ11 jack. The converse is physically feasible (the RJ11 plug is smaller than the RJ45 jack), which leads to the misconception that the two should or can work together. This is not actually the case. It is highly recommended not to use RJ11 plugs for RJ45 jacks.
Because RJ11 is not internationally standardized, its size, insertion force, insertion angle, etc. do not conform to the international standard connector design requirements, and thus cannot ensure interoperability. They even cause damage to both. Since the RJ11 plug is smaller than the RJ45 jack, the plastic parts on both sides of the plug will damage the metal pins of the inserted jack.