Being of the same weight myself, I would say:
The 141 is definitively too small for you as you don't yet master straps and harness. It wuold be very tippy even to uphaul for you, and quite a stressful experience.
For a 75 kg beginner in your position I would recommend a 130 liter board, i.e. with some 55 liter of plus volume. And I think the same is appropriate for you. You need to learn on a board with some 155 liter of volume, get lots of time on water, learn harness first and then footstraps. Preferably also to waterstart. After that I think the F141 could be a good next board for sails between 7 and 9 m2.