Op I would look online / on your work intranet for photos of previous events, to see what people are wearing.
I know you say that men will be wearing shirt and tie or just shirts, but that’s probably with a jacket. MHA / logistics / transport events are usually a sea of men in suits , with a collar and tie / open neck shirt / smarty chinos and blazer. With the occasional polo shirt worn with a company fleece with a logo on it 😁
As it’s a quite traditional and conservative industry and you want to fit in, I’d wear a blazer / jacket with a simple blouse / top / shirt underneath and whatever bottom half you feel most comfortable in ( the shape / scale of the trousers or skirt needs to work with the blazer. I agree with wearing flat shoes ( or only a slight heel).
I see you are very tall and slim, so you might have to try on quite a few jackets to find one that fits on the shoulders and has long enough sleeves.
If you buy one in a neutral colour you will be able to use it in the future ( I’d wear navy as I’m more of a blend in person 😳) .
If you are brave and want to stand out from all these men in grey , black and navy, then buy a bright colour !
In the unlikely event that you get there and it’s very causal and you feel over dressed, then you can just take off your jacket. Have a lightweight sweater / cardigan in your bag if you think you might feel cold.
I’m not very confident and feel that I’m a few pounds overweight and a jacket makes me feel more covered up IYSWIM. Also people mostly see your top half when you are sitting at meetings / conference table / eating etc.
Congratulations on being invited . I assume it’s because you are good at your job and they see you as promotion material.