Just as info for the "never heard of" people in this forum: Corona entry rules are checked by border police and followed up by state authorities: "in around 190,000 cases, administrative offence notifications were sent to the responsible fine authorities". In minimum case people must pay an expensive fine and can also end up in jail (fines from German Infection Protection Act).
Full text:
"In addition to their normal duties, the Federal Police checked more than 25 million travelers in the past year to see if they complied with the Corona entry regulations. A spokesman said in response to a query that "although the Federal Police are not health police," checks were made on each of these travelers to ensure that the digital entry declaration had been completed in full and correctly. In addition, the officers had checked in cross-border traffic by land, via the seaports and in air traffic whether the required proof - test result, vaccination or proof of convalescence - was available.
Only in the case of almost 226,000 travelers - or around 0.9 percent - was there cause for complaint. In around 190,000 cases, administrative offence notifications were sent to the responsible fine authorities of the federal states, i.e. as a rule to the health authorities.
According to the data, there were significant differences depending on the means of transport. While at the airports almost only every one thousandth traveler was found to be in violation, almost every twentieth traveler (4.8 percent) was found to be in violation at the land border."
Source: Tagesschau
Translated with www.DeepL.com/Translator