question about flash blocking content execution after 12th

Thankfully there are solutions.

To answer your question the block is the flash player and your browsers simply deciding flash wont function anymore. Ive heard it called a timebomb. Meaning after a certain date (The end of last year.) the program bricks itself. (Things might still work if your browser and flash version are both very old.) Even if you change your clock I hear future browsers from now on will be designed in a way that cant use plugins. Also internet sites tend to brick themself if your clock is wrong by too much.

The killswitch has been there for a good while. Cant remember when but I suggest finding an alternative to Adobe if you wish to continue using flash files. All the major browsers have collectively decided to prevent flash from running.

However with the right steps flash content can be played both offline and online. For offline you do it by loading any downloaded .swf files you have in a Standalone Flash Player aka Standalone SWF Player.

For online sites that have not purged its flash content you will need the site to update itself or use an alternative to the Adobe Flash Player.

For the standalone player you just need the right one and then load any swfs you have downloaded that dont need internet connection into the SWF / Flash Player. You can find the offical one here https://www.adobe.com/support/flashplayer/debug_downloads.html  Download then install "Flash Player projector" and then load your saved file with it. Drag and drop to play should also work.

For playing Flash on the internet flash sites will likely need to update themselves. There are many solutions in progress being worked on to do this but some sites are ignorant of any solutions and just purge their SWF content. Some sites have their site specific solution. For example Kongregate or Newground will ask you to download a certain player.

Many internet sites are using Ruffle.rs to take their swf files and then convert and play them into an alternate standard when the file loads. This is said to solve old security issues and play the swf file as normal without Adobe Flash Player being involved at all. Possibly even letting you play the flash file on your mobile device.

Ive had success playing Flash file in chrome by using SuperNova SWF Enabler.

There is a browser called Puffin that says it will let you play swf files. Ive not tested it.

There is also a flash archive that you can personally add to or request archive additions of that intends to let people play things from their archive. You can download their archive or just play what you want. It can be found here. https://bluemaxima.org/flashpoint/