Hello @jeanmartel,
do you use the SMARTS Query node and don’t mind to have two of them you could try the following:
with the first SMARTS Query node search for [R] (this will bring all molecules containing rings to the first out-port).
Then, add a second SMARTS query that searches for [x3][x3] and [x4][x4]. [x3] is any atom that has three connections to a ring (you will see this both in fused and bridged rings), but [x3][x3] searches for two of these atoms which are directly connected (so fused rings only). The x4 variant is needed for aromatic fused rings, where you would have four ring connections. Important: the wanted molecules are now in the second out-port, as the fused ones are in the first. I did not test the query for all possible molecules, so please check if the behaviour is as expected.
Best regards,
Daniela