Someone have experience with employment confirmation letters?

I’m my boss’s first remote worker, and my status just changed from „have-to-stay-in-office“ to fully remote

Neither me or my boss really know, what to write inside that „employment confirmation“

Should it be a letter style? (1 signature boss)

Or a agreement style? (2 signature - me and boss)

Applied in Frankfurt Germany, for DTV Workation.

Help appreciated 🙏🏽❤️

I currently working for a company which allows remote work up to 60 days in a year if you have the right permissions to work in the host country (either citizenship, permanent resident, or valid work visa), so the position is not completely remote. Is it sufficient if I submit a screenshot of the company's remote work policy with my visa application? Anyone face any similar situation?