You can use the toolchain list subcommand to list only the installed toolchains.
For example:
> nrfutil sdk-manager toolchain list
Version Toolchain
v2.4.0 C:\ncs\toolchains\31f4403e35
v2.6.0 C:\ncs\toolchains\cf2149caf2
v2.6.2 C:\ncs\toolchains\cf2149caf2
v2.5.0 C:\ncs\toolchains\c57af46cb7
v2.8.0 C:\ncs\toolchains\2d382dcd92
v2.9.0 C:\ncs\toolchains\b620d30767
v2.7.0 C:\ncs\toolchains\ce3b5ff664
v2.2.0 C:\ncs\toolchains\v2.2.0