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https://www.aptinting.com/automotive/kdx-anti-glare-mirror-film/
Might give the above a try, tons of stuff on Amazon as well.
I've been looking into updating the lighting on my 92 Saab and the options are pretty basic. I have one OG reflector and one newly resilvered one and although the new one is clearly brighter what's noticeable is the new high output lamps cast really messy beams most likely as the reflector wasn't designed for that output. I'll probably end up refurbishing the other reflector then using standard output lamps so it's as good as it should of been but still crap by modern standards.
Ditto LED replacement indicator lamps, very little diffusion as they're naked LED chips and without the fade incandescent lamps have makes them very spotty and jarring.
Another one in the 'constantly being pestered by stupidly bright lights in the rear-view mirror' brigade. Going off the sunglasses suggestion, is there not some sort of anti-glare film you could apply to mirrors to prevent the blinding?
Only other solution I can think of is: