[subject] + 只不过 + (是) + [verb phrase] + (而已 / 罢了)
[clause],只不过 + [clause]
只不过 means "merely, only, nothing more than". It goes after the subject, usually before 是, and makes what follows sound smaller than the listener might think.
The sentence often ends in 而已 or 罢了, which both mean "and that's all". They don't change the meaning, just lean on it harder.
At the start of a second clause, 只不过 adds a small reservation to something mostly positive. It is softer than 但是, and close to 不过 used the same way.
In the first use 只不过 follows the subject, like 只. It does not go before the subject.
The clause-initial 只不过 is the other use, and the clause before it carries the main point.