I’ve bitten the bullet and finally “upgraded” to OS 26 last week, thought 1/2 year is enough for Apple to make it stable enough (it’s not).
Here’s what I have hit:
1) upgrade from macOS 15 to 26.3 bricked my MBP (firmware failure). DFU revive kept failing.
2. iOS 26 (or watchOS 26) deleted all of my stored passes and loyalty cards in Wallet #dataloss
3. Most funny bug: the Calendar widget in Smart Stack on watchOS 26.4 keep showing *some* events with wrong start date (usually 12:00 but not always) while it’s correct in complications and inside Calendar app.