Can I react to Holding Point Scoring?

No, you cannot react to holding a point for scoring.

According to RiftJudge FAQ #2429 and RiftJudge FAQ #5620, scoring a point from holding a battlefield at the beginning of your turn happens automatically and does not trigger an ability, nor does it create a priority window. Because there is no trigger to respond to and no chain is opened, you cannot play reactions or any other speed of card in response to the score occurring.