DB has had similar offerings before, and also this time, they make it hard to get and hard to use.
Be aware:
The tickets are only available in ‘participating’ Edeka shops and not all Edeka shops. The list of participating shops is not published, nor is there an online function to search for one.
DB points out, that even participating shops may be sold out and that the offer is only available as a limited number of tickets. They obviously expect you to run around to different Edeka shops or at least call them in advance to ask if they are participating and still have tickets.
It is not really a ticket as the name suggests, but rather a voucher you can use to later pay for a proper train ticket. There is a limited number of seats on each train for Egal-Wohin-Ticket holders, so even if you have managed to find and buy a voucher, you have no guarantee that you can actually use it to book a ticket for the train you later intend to travel with.
It is not possible to check if seats are available for a specific train without actually having a voucher code. You have to buy an Egal-Wohin-Ticket first, to then later possibly find out that you can’t use it for the trip you have planned.
And finally, 39.90€ is not necessarily a very good offer for a train ticket in Germany. If you buy your regular ticket a bit in advance and can travel during off-peak hours, you can probably get a cheaper saver fare for most routes. I can for example now get a regular ticket from Munich to Hamburg (almost across the entire country) for 37.90€ if I book 6 days in advance, 27.90€ if I book 8 days in advance and 17.90€ 13 days in advance.