Which can be printed on paper?

For now. As an example, there are Amazon Prime discounts available at Whole Foods, and this QR code which asserts your membership cannot be printed because it embeds an OTP-like temporal code which changes every 60 seconds.

Any QR code which can be printed, can be copied. There's a vested interest for the operators of these systems to reduce the copyability of these codes (think: vaccine passports). Embedding a temporal code, changing the QR code every few minutes, and invalidating old codes, essentially OTP, is the most straightforward and industry standard way of doing this; it's inevitable.

This is true. I would need to print twice a week and I don't own a printer.

In the UK, you can have it posted to you, so you don't need a printer.

Does this work for a 'permit to enter' which is only valid 24hrs?

Only a CoronaCeck test result certificate is valid for 24 hours. Certificates of vaccination and recovery are valid for much longer (https://coronacheck.nl/en/faq/1-4-hoe-lang-is-mijn-coronabew...).

Are there places which are legally required to only accept test result certificates?

> Are there places which are legally required to only accept test result certificates?

Not in NL. Why does this matter?

For me, elective medical procedures and air travel required a recent (<24h) test result, vaccination was not sufficient.

Yes.