TL;DR: we need to remove support for M-strkeys (SEP23) from all the SDKs. If the SDK you are maintaining still doesn't have support for SEP23, you can ignore this message.
We have already reverted support for SEP23 in the Go SDK and the Javascript SDK. You can use those PRs as reference to do the same in your SDK.
SEP23 is still a draft and may not be promoted to final. Adding support for it means that users may end up storing M-strkeys, which can create a lot of problems if SEP23 ends up not being implemented. We are sorry we didn't identify this earlier.