Pages v 7.1 macOS Siera 10.12.6 iMac Mid-2011 (12,2)

I have quite a few devices that use Pages documents across iCloud, but the v7.1 on my older Late-2011 is stuck on version 7.1, although in App Store gives option to upgrade, but nothing happens. The problem is when I open the Pages document the holds a locked doc with usernames/pw to variety of websites it is read only; but, occasionally has an EDIT button showing. If I click on this I can edit. It would be useful to get a higher version of Pages installed and working on macOS Sierra 10.12.6.

I tried High Sierra and caused variety of problems and VERY slow. Best advice found from variety of sources says to stick with 10.12.6 with the HW of the Mid-2011 iMac 27"(12,2).

My new iMac 5k 27" Big Sur has Pages 10.3.9. Surprised the Pages documents in iCloud works fine across all my Macs and iOS devices, except the older iMac being usually read only, and such an older version of Pages. Suspect the next upgrade both iMac will be excluded, as the newer is Late-2014, and Big Sur listed it as the last it will work with.

Any advise would be appreciated.

I use the 2011 iMac in target disk/Display mode for DAW work in LogicPro, and need only a plain thunderbolt 2/1 cable. Considering a new iMac 2020, or wait for the M1; but concerned this will make useless both iMac I have now.

Been with MacIntosh since early 80's, as only platform supported musicians. PC's did not pay attention for over a decade with DigiDesign/Opcode combo multitasking first supported, Audio/MIDI Sequencing required 2 different Apps, has had not yet evolved into one App at the time, and quite difficult to get working. At least there was agreement on MIDI implementation on all devices early on.

Best,

Seth