Maybe we should change "packets of other encryption levels" to "types of packets."
In RFC 9000, we talk about "type of packets" when clarifying when the frames can be used; see section 12.4.
With the understanding that this is not the problem that the PR is trying to address, it might make sense to adjust the phrasing.
This applies to the paragraph right above as well. It would suffice to drop the MUST NOT there, just state "All the new frames MUST only be sent in 1-RTT."
As raised by @kazuho in #236: