Отключите EOL uninstall ворнинги:
    Disable auto updates when installing
    Add "EOLUninstallDisable=1" to mms.cfg in C:\WINDOWS\system32\Macromed\Flash
    (C:\Windows\SysWOW64\Macromed\Flash on 64-bit)

---

Обнулите сроки для временной бомбы:

Time bomb trigger is the timestamp 1610409600000.0
encoded in double precision floating point (0x42776f3e46400000):
    00 00 40 46 3E 6F 77 42
replace with infinity:
    00 00 00 00 00 00 F8 7F

C:\WINDOWS\system32\Macromed\Flash
(C:\Windows\SysWOW64\Macromed\Flash on 64-bit)
    Flash32_32_0_0_453.ocx (offset: 453: E1D968, 465: E1DBD0)
    NPSWF32_32_0_0_453.dll (offset: 453: E3A2E0, 465: E3A32A)
    pepflashplayer32_32_0_0_453.dll (offset: 453: CBFCE0, 465: CBFCB8)

C:\WINDOWS\system32\Macromed\Flash (64-bit):
    Flash64_32_0_0_453.ocx (offset: 12AF6A8)
    NPSWF32_32_0_0_453.dll (offset: 128FBD8)
    pepflashplayer32_32_0_0_453.dll (offset: 15F6C30)

NOTE: Flash32_32_0_0_453.ocx (and Flash64) will always be write protected
    - rename it to Flash32_32_0_0_453.bak
    - save edited copy as Flash32_32_0_0_453.ocx
    - to delete the backup file:
        - properties > security > advanced > delete the "DENY Everyone" permission



from: https://superuser.com/questions/1616866/use-flash-player-after-12-jan-2021