Yes it looks like this is an issue concerning the new update and as of right now, I've reverted back to the previous software until someone finds a fix for this. I too use my Alarm daily and it has messed up my last two days of getting up for work.
Alarm also not working here - can't even open the app on the watch.
I'll save everybody the troulbe of bothering with Samsung Customer Service... they'll give you to some low-level well-meaning lackey who will suggest you reset your watch (won't help); factory-reset your watch (will only waste more time); then will perhaps suggest you take it into a local Best Buy who can "reflash the update" - an endeavor that even if it would or could help will be fruitless: Nary a single person at the 3 Best Buys I called had any idea what I was talking about and all suggested I send in my beloved $400 watch to Samsung who would, in all likelihood, have to wait for the same update everybody will (thus unloading your watch on them for several months).
To the previous poster who indicated that he'd downgraded his OS - I think I speak for everybody else that will be on this forum today and in the coming days in asking you to share with us how that's done - the delightful people at Samsung's customer service said that it can't be done (which, as a software developer myself, I find utterly ridiculous).
I read a few forums on XDA and decided (being the tinkerer I am) to downgrade the OS on the watch. This is *not* for the faint of heart as you can easily "brick" your watch (render it useless although often recoverable). You have to download the most recent (pre-OneUI) firmware (in my case, for Verizon, it was R765VVRU1CRL8). Then using an application you can find on the internet (most easily via a Youtube video regarding downgrading the Gear S3) called NetOdin, you flash the **model and carrier specific** firmware for your watch (this requires a wireless wifi connection). Again - if you follow the XDA post on the subject and have the correct firmware you'll be fine. But if you're not comfortable with "rooting and romming" type stuff - I'd just wait until Samsung decides to push out a *tested* version (which, if history is any indication, won't likely be for a few months).
I'd venture a guess that many - if not most - of the owners of a watch of this caliber are at least tech-savvy (and knowledgeable) enough to have tried a reset before thumbing the pages of the internet in search of a fix. I tried a reset - twice. I tried unpairing the watch and doing a reset both from the recovery menu and the native menu. Neither made the alarm app work.
Reset for my watch fixed the alarm app, as well. Using the Samsung wearable phone app: I tried removing the app first, apparently it is a system app and cannot be removed. I tried doing a restore as well, for just the alarm app. This completes but does nothing to change the loss of functionality - so I tried the full watch reset. When the reset completed I did not restore right away and when I tried the alarm app it was working as expected. Then I restored to my last backup on May 20, 2019 and this completed without errors and the alarm app was likewise, also working again.