Audio-syncing is a definite issue and one that's exercised me somewhat over the last few days.
I don't know of any device in the 'less than 4 figures' category that can achieve onboard hardware syncing. Some people seem to solve it by routing their mixed audio through a camera and having that camera' locked' as the audio source, whatever the pictures are doing. That works well and keeps sync, but of course is dependent on the chosen camera having a decent audio set-up.
I had considered going for some sort of hardware delay-line... Lindy and B..ringer have some units at around £70 - the B being much more versatile with all the other stuff you get as part of the package.
I asked a friend, who has a very sophisticated live-streaming set-up for reviews and other stuff, for his thoughts... He pointed out that the software available with all of the ATEMS has a means to dial-in audio delay as well as things like EQ and compression. However, for my application I really need multiview/preview facilities... the cheaper ATEMs don't have any form of preview/multiview output...

Interestingly, despite all the gear at his disposal, my friend uses the 'audio thru camera' technique.
I could be mistaken, but I think if you use OBS etc as a streaming front end then you can apply the delay there... but I want to keep things very simple so shall probably eschew that approach and use a platform that just recognises the streaming switcher as a webcam.
As far as people noticing sync issues, I'm not surprised that many people don't notice it. If you're watching on a phone or tablet you may not be so aware and, as we know, we audio people can be shuddering in our shoes at noticed audio issues whereas others around us are responding with 'what issues?'

Thus far I've been using a couple of HDMI-USB devices to link my camcorders into Zoom etc and a separate input audio interface (as opposed to my standard fare - long story!) for mic(s). Excellent results that way... as long as I ignore sync. My experience indicates that at 25fps the video has about a 3-frame lag, but it can vary...