Manager is so fucking anal!

I joined probation in September last year. Love the job love working with people (all be it stressful at times!) I have a manager who is the most anal man I have ever met! He has extended my probation period 3 times due to not hitting the PQIP targets (tasks to be completed by X month everyone on my programme got the same extension), then again as he was unhappy with my grammar and a third time for you guessed it GRAMMAR! Back story I'm dyslexic and use voice software (it doesn't insert punctuation for you) I explained this and started to use words read aloud which is a game changer! But still he's not happy he has nothing else to pick at but THIS! my probation review is at the end of this month. I have a feeling he's going to fail it for grammar. Any advice? I've already been to seniors (no help there) Unions a bit shit I don't want to post in ABLE (he's a member) I have reasonable adjustments it took 7 months to sort them!

so I'm hoping the civil servants of reddit can help/advise 😊