You can use the toolchain search subcommand to search for all toolchains, installed or available for installation.
For example:
> nrfutil sdk-manager toolchain search
Version Status
v2.9.0 Installed
v2.9.0-rc2 Not installed
v2.9.0-rc1 Not installed
v2.9.0-nRF54H20-rc1 Not installed
v2.9.0-nRF54H20-1-rc2 Not installed
v2.8.0 Installed
...