Although it was out there, if you knew where to look, IBM just published the traditional EoS for Power 9 (first generation) products : https://www.ibm.com/docs/en/announcements/services-withdrawal-discontinuance-service-select-power-systems-products-replacements-available

Remember that IBM i 7.5 (V7R5) is the last release supported on Power9 …

Start planning for an upgrade !

[UPDATE]

This advice is about the first generation of Power9 systems (MTM 9009-xxA).
It is obvious that the second generation (MTM 9009-xxG) will be the next one … Soon !