It’s actually crazy how this issue hasn’t been fixed as of 5.3.2, or a solution found. Makes creating landscapes or placing foliage etc nigh impossible.
Weirdly enough RediOne1’s advice of using the trackpad worked at first, but then it reverted back to the high sensitivity again. Maybe restarting the engine would work, but I can’t do that seemingly every few minutes.
EDIT: so far the only solution is from May 2018 by the OP: switch to windows. I just picked up my first tower in years and will be deving on there from now on.