Regarding the incompatibility of using the viewport menu to switch between ik/fk when mgear 3.7.9 uses the old version (<3.7.9) rig assets in the pipeline, is there any other convenient method besides rebuilding the rig assets?
for IK/FK switch you can use the synoptic or Anim_picker
Thank you for your quick reply! 
This plan is in my plan.
I know that in the new version, in order to better track the IK/FK match, you have defined a brand new way, which makes the old version encounter obstacles in the way of querying to obtain attributes and targets. Have a small idea, whether it can be in the query mode Added to determine the mGear version to tell mGear to use the new tracking method or the old tracking method to obtain compatibility between the new and old versions?
I personally like the viewport menu function key, which improves the efficiency of attribute interaction. Compared with AnimPick, it is more convenient for quick operation of rig asset attributes, so I prefer the viewport menu function key. 
I haven’t closely looked at the difference yet, but maybe instead of rebuilding the rigs, you could just look at the attributes that get added in the new version, and run a script to add those attributes/connections to your older rigs.
Having a query to determine the rig version, and selecting the correct version of the function would certainly be ideal.