Just like in all API implementations, MinClientVersion and MaxClientVersion in ib_insync are constants. They are attributes of the client class and while I am not a Python practitioner, I am sure it is straight forward to extract their values in client programs on-the-fly. Along with the server version.
I also did some more digging on and it looks like what you are doing requires a TWS of Version 979 or above. TWS 10.10 or API level 165 are not required.
TWS 10.10 and API level 165 are required for crypto support and fractional sizes in market data related objects (Bar, TickByTick*, ...)
Not sure what to suggest other than maybe going trying a stable TWS below 10.10 (say 981.3d). We had lots of issues with 10.10 versions of earlier this month.
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