DNS typically uses UDP, and switches to TCP if the packets become too large.

Previous recommendations were to use UDP packets up to 4096 bytes, and then switch to TCP. This has been found to have some issues, as large UDP packets are sometimes filtered out.

DNS Flag Day 2020-10-01 therefore recommends that the maximum UDP size is set to a value that minimizes the need for fragmentation. This, of course, means that TCP will be used more extensively.

Abundos name servers are, of course, updated and running with the new recommendations.

Read more about DNS Flag Day 2020 here https://dnsflagday.net/2020/ Here you can also test your domain and name servers to see if they follow the new recommendations.