The feature enhancement of the notes app in ios 15, ipados 15 and macos 12 may cause problems in older versions of the operating systems: as soon as keywords (#tags) are added to a note, it apparently cannot be displayed longer with older versions of the app. The restriction also applies to the new @mentions, which can be used to contact other users of a shared note.
Notes disappear from older versions
The youngest versions of ios and ipados 14 (from 14.5) and macos big sur (as of version 11.3) lacks the new tag and mentions features, but is still able to open and display notes in apple’s pre-installed app, as developers report. The keywords are simply listed in the text; the option of sorting notes by keyword is only available from ios 15 onwards. However, on older hardware or when remaining on older operating system versions, such notes are hidden.
In the future, this will be problematic for users who, for example, still use an iphone or ipad with ios 12 or a mac that cannot be updated to at least macos 11 big sur.
Upgrade required – if possible
Apple draws attention to the problem with a warning dialog that pops up in ios 15, like 9to5mac noted. This also lists devices linked to one’s icloud account that are not compatible with the new features. An upgrade is required on this hardware to view the notes. If this is not possible, apple notes the device cannot be updated to a required version.
A fallback option remains on the older devices to view the notes as a web app in icloud.Com. Official system requirements for the note app of ios 15, ipados 15 and macos 12 apple has not yet named.