At the time of this Writing 12-08-2020 I can't say for how long after this, because things always change.
So when you buy a New Old Stock camera one that someone might have had as a Gift and never used or one that someone bought a few extras as backup in case they needed them or what ever reason your able to buy a Camera from years gone when it comes to FW updates please note that the Camera when setup right once you go into Setup it will prompt you to DL and install the FW update. Take Case in point doing some work with one of my cameras I installed an older FW from 2016 and package data was 00009 and the camera says the update Version is 00011. So that means between the 2016 package and the 2017 package there was another one between. But the 00011 was the last non JS FW found to be stable..
Why this matters? Some people that are going to do the Update might be thinking that it is going to update into the 2020 FW or last FW that the camera has on the Website and The ones that want that FW will need to Update that FW from Downloading it from the Amcrest Firmware Website.. However if you want the Last FW that the 841 had before the JS Software you can just do the Auto Update off the camera and it will change from the one you had maybe it was 00004 or the first 00001 even as I have had some of them cameras in my lineup of 841's
So if your looking for just non JS fw the last one that was done and is setup to update a camera too is a different FW number from your normal but I assure you it is for the 841 v1 and v2 and that is 2.520.AC00.18.R, Build Date: 2017-06-29 when the camera on going to Setup after logging into the WebUI if on older then that FW like V2.420.AC00.16.R.20160909 So don't worry about the different fW number it seems to be only that 2017 version that it changed from 420 to 520 where the new 2019 and 2020 versions are back to 420 and only way to know now what update your on is by the last of the FW numbers of build date..
As of now it is said from time the JS FW came out that once you go to the new 2019 or 2020 FW you don't want to try to down grade your camera to older FW because you might damage the camera to the point it will no longer function.
So after some more testing and playing around I found some things out that might be important to note here as well...
If you do a Wifi only setup when you log into the Camera over the Cell app it won't prompt you to upgrade. Also while still in Wifi if you happen to log in on the WebUI again it will not prompt you to upgrade to the new FW without being either updated in the Network settings of adding DNS info under TCP/IP tab of Networking, Change the Wired/Default drop down to wifi you can make it default if you like but that isn't what you need what needs to change is the bottom 2 lines setup for 8.8.8.8 and 8.8.4.4 and save/apply
Now I don't know how long it will take for it to offer the update after making that change.. I do know that once made I tried to press the Check for update and log out back in and no offer However I did a Power Cycle of the camera and after logging back into the WebUI and going to setup it right away prompted me to install a NEW fw..
PLEASE NOTE DOING THE FW UPDATE THIS WAY WILL ONLY TAKE YOU TO THE LAST KNOWN STABLE NON JS FW IF YOU WANT TO HAVE JS FW PLEASE GO TO THE FW PAGES OFF THE AMCREST WEBSITE
Edit: Also after a few more test.. Also found that you will want to change your wifi setup for DHCP to Static with the changes to dns because it seems in my setup anyway after a reboot of 2 times the DHCP server don't retain the DNS info and it goes back to what the server sets.. So Wired or Wireless always make sure to setup Static IP for best Results.. It will also prompt you to update to new FW even from live view page as well you don't always need to just go to setup for it to offer you the update. Just FYI