Since Brexit happened and everything has been firmed up, UK nationals wanting to live in Germany require a residence permit. That process is surprisingly easy and straight forward: studying in Germany is possible and simply requires a student visa, the same applies for vocational training. If you would like to set up a business, either self employed or incorporating a business, then you can apply for a permit too. Researchers at universities are also welcome with an offer from a university. If you would like to work in Germany and done vocational training or have a university degree then you are good to go after you’ve applied for a job seekers visa. Head over to Germany and find a job which then allows you to apply for a resident permit which is employer binding. With a job offer in your pocket, you can apply for a permit straight way. However, without vocational training or a university degree, it is near impossible to obtain a resident permit in Germany. UK degrees now need to be officially recognised in Germany, health insurance is needed which you get once you are working or studying. Speaking German to level B1 is a requirement for some permits. It goes without saying that you ought to speak German in Germany! Check out this comprehensive website for further info: https://www.make-it-in-germany.com/en/
Should you need to travel to Germany for business or a visit, then you wont need a visa.