The above is not technically accurate from a point of view of support for this flow in ADFS connections; although there are indeed considerations around usage of ROPC grant, at this time and per (Call Your API Using Resource Owner Password Flow) it may be possible to use this flow with:
Make sure your connection is capable of authenticating users by username and password (for example, database connections, or AD/LDAP, ADFS, or Azure Active Director enterprise connections).
Due to how this flow works there may be additional requirements, in particular, the ADFS instance would need to be accessible/reachable over the Internet and be configured to support this flow as well, but from a technical point of view this should be doable because although I haven’t tested this recently I believe the documentation is still accurate.