Peak TX current of LoRa RFM95W
To be blunt, that's really not a great idea, as the current demand is far in excess of what a coin cell can supply.

Typically sensors are designed to run for a long time, and so will use higher capacity cells, which are typically able to support proportionately higher peak loads as well.

If you really want to try to design something that can achieve a very short number of transmissions off an undersized battery, you probably need to use a large capacitor to provide the transmit current.  But realize that packets of hundred of milliseconds are common (or well over a second in Europe), so that's going to be a fairly large capacitor.  You may even want to go so far as to to have MCU logic which pre-charges the capacitor only in preparation for a transmission - typically the packet duration ends up being calculated anyway, so you could anticipate the overall energy requirement and factor that into the preparation.