I had a similar problem, trying to make my Macbooks less glare-y outdoors. I tried a variety of solutions (like sunbrellas and screen enclosures) but they didn't work very well.
Having tried various no-name anti-glare protectors off Amazon that didn't work very well, eventually I found a small US-based company that does custom-cut anti-glare protectors with actual optical analyses: https://www.photodon.com/
They primarily sell industrial, I think, but also will cut a sheet for you to spec. They have common device types/sizes listed, or you can provide detailed measurements and they'll do a special cut for you, including for curved monitors.
There's a video showing their different types (https://www.youtube.com/watch?v=QhIZPO9oMGY) and a quick comparison sheet (https://www.photodon.com/Film-Comparison-Print.pdf), or you can order a sample kit to try different kinds (https://www.photodon.com/p/sample-screen-protector-privacy-f...) to see what suits your needs the best.
Personally I got the MXG 85% glare reduction film (https://www.photodon.com/Anti-Glare-Screen-Protector-Specs-M...), and it's worked VERY well on both laptops it's installed on, with minimal change in clarity (it's hardly even noticeable, but really really helps with glare and specular lighting). I notice that it's not immediately available on their website; maybe they replaced it with a similar material but with blue-light blocking (AGB)?
Their support is US-based and very helpful, if you have any pre-purchase questions.
I'm not affiliated with the company, just a very happy customer who's grateful to have found them.