Google has repeatedly invited Apple to support the RCS protocol on iMessage to standardize cross-platform messaging. At this point if a message is received from an Android device, iMessage users can see a green text balloon. According to a 9to5Google report, Google has confirmed that Apple will finally support RCS starting this fall, around September.
The Google Messages page has the text "coming to iOS in the fall". With RCS support, more secure messaging with encryption as well as message notification support has been received, has been read and can be replied to with a reaction can also be supported on Android and iOS devices.
The existence of "green balloons" in iMessage is one of the reasons why Apple was sued by the United States government for being accused of "monopolizing the smartphone business" in the country. Various ecosystem barriers also forced them to make changes to meet the requirements of the DMA in the European Union (EU).