As for COVID related regulations, the Harz region was 2G+ while we were there. It didn't impact my husband and I because we're boostered, so no need to show a negative COVID test. The TI office told us the kids would be ok without a negative test because they'd so recently been double vaxed. However, that did cause some confusion in Wernigerode especially since German children just became eligible to be vaccinated so places aren't used to seeing kids with two vaccines. My guess is by the rules, we probably should have had the kids tested. But, ultimately we were never turned away from any establishment.
We went back to our friends in the Frankfurt area for New Years and spent a couple more days with them. I think my most touching memory was of New Years evening. A neighbor somehow got fireworks (even though selling them was banned to prevent NYE gatherings). We got to see a spectacular display from the comfort of our friends' back porch, toasting with champagne together, and listening to the church bells ringing out between bursts of fireworks. What a beautiful, hopeful moment after such a long, challenging couple of years the world has faced!
Anyhow, back to pertinent information. We used the Binax test kits that you do from your hotel/home with an online proctor. We chose that since we weren't sure if places would be open on Sunday of the New Year's weekend. It was cumbersome. Took about 25 minutes per person. Mine took over an hour because the internet dropped and I had to start my wait time over. All together it ended up eating up a large part of our last day in Germany. My test results never were delivered to the app though I did get them by email. My husband and kids had a smoother experience and all results were delivered properly. Thankfully, only having the results via email was fine for travel purposes. I'm not sure I'd choose that option again. But it did save us the extra step at the airport.
Our journey back was equally smooth. No issues with paperwork, test result documentation, etc. The Frankfurt airport wasn't that crowded. It took less than an hour and a half for us to get through all the steps of checking in and to our gate. We were there much earlier than we needed to be. Thankfully, we also had no issues due to all the flight cancellations that were happening over the holidays!
We really, really struggled with whether or not to take this trip. We booked plans and cancelled things SO many times due to the constantly changing situation leading up to our flight date. In the end, we just went for it and adjusted as needed on the fly. And I have no regrets. It was a beautiful trip spent reconnecting in person with loved ones and it's a trip I will always cherish even the more after all the challenges and disappointments we've endured over the past two years.