Is fresh mulch really that bad for plants? (Nitrogen drawdown)

New gardener – I see online that fresh mulch is a problem for plants. I got free mulch from council and really want to use it and not worry..

The mulch I have previously purchased seems to be ok for the plants. I can’t know for sure since I have nothing to compare it with since it’s my first garden (I.e. maybe my plants would be doing better with other type of mulch)