Yes, Ireland can still qualify, via the play-offs of course. If Ireland beat Armenia in Dublin tonight and Portugal win at home to Hungary by a couple of goals, Ireland could move from fourth to second in the table and then chase down maximum points in the remaining games, at home to Portugal and away to Hungary next month.
The Champions League was revamped before the 2024-25 season with a new 36-team league phase. In the expanded tournament each side plays eight different teams - four at home and four away - in the league phase. Teams who finish in the top eight automatically qualify for the last 16, while those placing ninth to 24th will compete in a two-legged knockout play-off for the chance to join them.