Hi barry,
the balena Fin needs about 3 Watts alone under heavy load ( Why is the balenaFin right for fleet owners? Part 2: Power ). I don’t know how much the RAK2245 will be drawing, but I guess it would be enough. However, to use PoE you will need to add a PoE Hat as well, so that the PoE functionality on the Fin can be used. Please be advised of the clearance issues handeld here: Fin v1.1 PoE hat clearance issues - #15 by mycroes
There is also a way to passively gain access to PoE by using an intelligent PoE splitter, attaching this to the Netgear Switch and inserting the “only data” ethernet into the Fin and the power via e.g. the phoenix connector, but its a bit more fidly, adds to more bulk and cabling and maybe not as safe as just using a PoE hat 
Cheers
Nico