You can add a substring with any value at the end of the list subcommand to have sdk-manager list only SDK versions that include the value you provided. This is referred to as [SEARCH_SUBSTR] argument by the command help.
For example, the following list command with rc string at the end will display only the versions that include rc in their names:
> nrfutil sdk-manager list rc
Version SDK Toolchain
v2.9.0-rc2 Not installed Installed
v2.9.0-rc1 Not installed Installed
v2.9.0-nRF54H20-rc1 Installed Not installed
If the substring is not found in the version names, the command will return an output similar to this one:
No SDKs with "rc" in the name installed