You can't fix Monks. Even worse than Fighters, you can mathematically prove Monks are terrible, and not only do defenders of the class go on about their incredible value as skirmishers and damage dealers, you'll have DM's with horror stories of their entire campaigns being ruined by a Monk player calling for the blood of anyone who would dare give them even a minor buff.
Even WotC knows the class is in bad shape, when Tasha's gives them "alternate abilities" that the DM can decide to just give them for free, without any cost!