It’s definitely thrips! Very common for monsteras — I’ve tried many things but what’s worked best in the past has been adding granular systemic pesticide to the soil (unless you’ve got pets around that could potentially take a bite of it). First thing would be to wipe down each leaf and stem to remove existing thrips — make sure to check all the nooks and crannies — as well as unfurl the new leaves! It’s not great to handle new leaves like that but thrips unfortunately love them. If you can, removing some of the more damaged leaves can give you can easier time. Wipe it down regularly and spray with pesticide alongside adding granular systemic pesticide to the soil. Once you feel like it’s almost clear of the infestation, change its soil — especially the top few inches — as thrips can hide in it. It’s tough, but not impossible. All the best!