Have been in Germany for only three days and have come across 4 establishments that were cash only; restaurant, cafe, two ice cream shops. That’s more places than my entire 25 day trip to Spain last year. Have both. We use a CC when we can, but have cash in case the hostess says cash only.
We were at an ice cream place after dinner tonight and an individual had to ask a friend for cash when the gentleman behind the counter said cash only. One public toilet in town took coins. This observation may not be totally accurate, but the more touristy towns will have more places that accept cards. More rural and less touristy places is where you’ll find more cash only places.
When I’ve charged my hotels and at restaurants, the default has been charge in Euros, but I always check the machine.