I don't own a Fathom E+3 but from pictures available on the net, it appears the bike is not designed for a rear rack. A universal rack such as this one may be adaptable:
Amazon.com : West Biking 110Lb Capacity Almost Universal Adjustable Bike Cargo Rack Cycling Equipment Stand Footstock Bicycle Luggage Carrier Racks with Reflective Logo : Sports & Outdoors
www.amazon.com
If what you want to carry is less than 25#, you could also use a seatpost only type rack:
This type has no standoffs to keep panniers from contacting the spokes though.
Amazon.com : CyclingDeal Bicycle Bike Alloy Seatpost Mount Rear Back Cargo Pannier Rack - Universal Mountain or Fat Bike Luggage Carrier - Lightweight : Sports & Outdoors
www.amazon.com
I suppose it depends on how much you like the Fathom. It is a sharp looking bike. Both these adaptable racks would probably work but they can make it difficult to remove or adjust the seat height.
Perhaps a Fathom owner here can provide more information.
I have the 2020 FathomE+ 1 Pro. It does not have any attachment points for a rack. My LBS has ordered a Thule Tour Rack for me. Hopefully it arives next week.
+1 on the topeak Tetrarack. I have one on my Trance and one on my Haibike Full Seven and they work well. While it says you can put a lot of weight in it, I am not so sure about that for long trips. I'd go to an Old Man Mountain rack and a Robert's Axle project for really heavy packing.