Those are not real screws. You can find several images onlines on how it comes apart, like this: https://poshmark.com/listing/Apple-Watch-gold-metal-case-63b8d998ffb5d0b96ff9b1f2

Just use google reverse image search for more information.

It’s more like a physics problem than a software problem. Imagine if Apple decreses the sensitivity on wrist detection to make the Apple watch experience better for tattoed users, so they decide to ignore some instances when the light emitted by the sensors can’t provide enough feedback because they are absorbed by the dark spots. That would overall make the safety features of the watch worse, for example in theory someone could just snatch the watch off you on the street, then fasten it on their own wrist and carry on with it, using ApplePay and such… so overall it’s a difficult problem to handle, it’s no wonder Apple still could not address it after releasing 9 generations of watches. It’s not because they are lazy to release a simple software patch. You can influence them to maybe shift priorities and work on this issue more by submitting your feedback, that’s about all you can do right now unless you are willing to remove or lighten the tattoo.

Almost everyone with tattoos has experienced this issue, probably you have already seen the hundreds of posts about it for the past 7 years, but the severity of the problem with wrist detection varies based on the darkness, technique, age, etc. of the tattoo. If your previous watches cooperated better, then it’s probably because the sensors on the back of the Ultra are situated a bit differently, (same circular layout, but not the same) so now the sensors are being blocked more by the pattern on your wrist. Also, the Ultra is heavier than previous models, so based on how you hold your hand during the workout, if the band is not tight enough, the watch body may slightly shift away from your skin instead of laying flat, making things worse. In any case, the optical sensors on the Ultra in this regard were not made better or worse for tattoo users. Auto-pausing the workout is not what happens to you, that’s a separate feature you can disable in settings under workout. Your workout tracking fails because wrist detection fails.

Try wearing different bands, try wearing your watch further up or down your wrist or switch hands if that’s possible for you.

It’s not true that Apple does not care about the security patches of Series 3 watches, they have just recently released an update for watchOS 8 this August, 11 months after their last update. https://support.apple.com/en-us/HT213808

None of our devices are 100% safe at any time in this world but I don’t think you are at an increased risk because of the Series 3 watches. I have a cyber sec expert in my friend group, they used to show me some terrible exploits that Series 1-2 watches had been vulnerable to in the early days (not anymore!) and those looked terrifying but all in all, but it’s extremely unlikely that S3 watches will be the target of any similar attacks in the future. (In my own opinion based on what I know)

Just keep your passcode on (I suspect your work profiles already require you to do this anyway) and don’t worry too much about it.

Look out for any popular iMessage scams though if you have cellular models, at my cellular provider we are dealing with some issues currently that targets the technical phone numbers of watches which work in a way that only the watch receives certain iMessage scams and none of your other Apple devices where you enabled iMessages. However, these are not only targeted at Apple watches but any device that use with a number share SIM card (physical or virtual), but I thought I would mention it since it’s a much more realistic threat these days.

You’ll find more users to help with this topic here r/watchOSbeta

No

You can try this: https://www.reddit.com/r/techsupport/s/eIAXXZmllY However as far as I know, if it really has a demo/display software loaded on it, a reset won’t do anything for you, only Apple can fix it for you, but they won’t do that because I suppose you can’t really prove ownership via this transaction, moreover, you can even get into an undesirable situation due to the grey background of this watch. Since the person blocked you immediately, I think they already knew that the watch was unusable. I know you may feel it’s unjustified that you already have the tech and can’t make it work, but the security measures are in place exactly for this reason, to discourage the theft of these devices.