The ending of Hobbs & Shaw removes the virus from Hattie Shaw, ends the immediate threat, and leaves one larger threat standing: Eteon. Brixton appears to die after the Eteon director deactivates his systems from afar.
Here is how the finale is built, step by step. The only way to take the Snowflake virus out of Hattie is a device at a facility in Chernobyl. Professor Andreiko is killed there and the device is damaged, so the story cannot end at the facility. It has to move to Samoa, where Jonah Hobbs repairs the device. The final act exists because of that repair, and the Hobbs family traps buy the time it needs. Brixton recaptures Hattie by helicopter, and Luke Hobbs and Deckard Shaw bring the helicopter down. Per Wikipedia, the Samoa scenes were shot in Kauai, Hawaii, which stood in for Samoa.
What does the director's message mean? The Eteon director's message shows he knows Luke Hobbs personally and wants to recruit Hobbs and the Shaw siblings. Opinion: Brixton's shutdown reads as a statement about how Eteon treats its own enhanced soldier, as a part that can be switched off, and the recruitment offer turns a one film mission into a standing invitation. That is why the story closes with the heroes together and the door open for more trouble.
Hobbs also reconciles with his family in Samoa. One reading is that this is the emotional finish of the story: the repaired device and the family traps only work because the Hobbs family is back in the same room.
How does it compare with the rest of the series? The Fate of the Furious and F9 sit on either side of this film in release order (it is ninth, and the only spin-off among the 11 films). No sourced reporting links this ending to the story of F9, so the open threat should not be read as a setup for it.
The post credit scenes add a few loose ends: Victor Locke, played by Ryan Reynolds, calls Hobbs about a more dangerous virus. TMDB credits the same actor as the Eteon Director, but no source explains what that overlap means, so it is not treated as a plot fact.
Will there be a follow up? No sequel to Hobbs & Shaw has been officially announced, so the open ending is a story beat, not a confirmed plan.