Some comments on how "closed borders" work further south.

Flying to BUD - after deplaning there are 2 checkpoints for "exemptions". I had a business invite (simple letter, signed and stamped by the partner) It was a quick look and "Have a nice day" No tests or anything asked for. Friend's kid came to visit, she was put in home quarantine, she uploaded the required 2 negative PCS results on day 2, never heard back, so she went ahead with her life. Nobody ever checked if she was quarantined.

Driving from HU to SK over the Danube (supposed to have some official (!) proof of exemption from SK entry ban) - no checks at either end (actually no police presence at all). I saw the HU inbound lane had one policeman stopping some cars inbound.

Driving from SK to HU (other, small crossing) - neither side manned, drove straight through. Totally 2019 feeling.

Relative's friend driving from HU to DE via AT - not once stopped until home, just drove the Autobahn all the way.

Colleague in SK says, that get visitors from NL, BE, etc, all of them driving, because nobody ever stops them. Similar stories from the HU-RO border, with very light check HU inbound, none RO inbound (aside from the obvious passport/ID checks)

Let's see how HEL compares tomorrow