Factory Reset and some questions

Right, so that explains how I must be getting better action from apt now, as far as non-netgear repos, but I think there is still a problem with netter's repo?

E: The repository 'https://apt.readynas.com/packages/readynasos 6.10.9 Release' does not have a Release file.     
N: Updating from such a repository can't be done securely, and is therefore disabled by default.                  
N: See apt-secure(8) manpage for repository creation and user configuration details.                              
W: GPG error: http://archive.kernel.org/debian-archive/debian jessie Release: The following signatures were invali
d: KEYEXPIRED 1587841717                                                                                          

Also when I try to install build-essential, I get the following error at this point, which makes me wonder if somehow when I did something earlier, some non-netgear version of libc-dev got installed or something, or its not actually trying to fetch from netgear's repo even now....the build-essential, which I seem to recall needs to come from there, but it was a long time when when first set that up on this machine, years and years ago.  Can't remember what I did exactly.

root@webman:/home/sjs# apt install build-essential                                                                
Reading package lists... Done                                                                                     
Building dependency tree                                                                                          
Reading state information... Done                                                                                 
Some packages could not be installed. This may mean that you have                                                 
requested an impossible situation or if you are using the unstable                                                
distribution that some required packages have not yet been created                                                
or been moved out of Incoming.                                                                                    
The following information may help to resolve the situation:                                                      
                                                                                                                  
The following packages have unmet dependencies:                                                                   
 build-essential : Depends: libc6-dev but it is not going to be installed or                                      
                            libc-dev                                                                              
                   Depends: g++ (>= 4:4.9.1) but it is not going to be installed                                  
E: Unable to correct problems, you have held broken packages.                                         

I remember seeing another error at some point that said something about me having some netgear version of one library and not compatible with a non-netgear library or something in build-essentials, etc.. I"m not really sure what is wrong or how I can set this up for compiling again...

But anyway after turning off the need to authorize, it did allow nzbget to install correctly and now I was actually able to use apt to install a couple things like python2, so its progress, and the 'apt list' is MUCH much longer after having done that, but somehow I feel I might have earlier installed something when apt was broken, that has now put my libc stuff in a broken state.  Any advice or comments about that?

So if I can get python3.5+ on here again like I had before I'd be able to ressurect Medusa also, which would be tremendous.  I will either have to compile it, if I can bet build-essential installed and working properly...or...there is someone out that that has a Jessie version of python3.7 in apt repo form, that I might try to install...  so..things are looking up to get this back to where I was before, despite deprecation.

have the following working again since factory reset on 6.10.9:

1. idrive backup
2. shellinbox 2.14 
3. smbplus
4. nzbget (updated to most recent version also)
5. python2
6. nodejs
7. vim (newest from jessie)
8. latest plex server
9. ncdu
10. htop
11. iftop

Only other thing I really need to get back to what I was before factory reset, is medusa...which needs python 3.7 for a much more up to date version of medusa compared to the original App Store version I had in there.  The App Store installer will setup a frontview icon for starting and stopping it and launching it quickly...but medusa has substantially updated since then, so I basically reinstalled medusa using ssh, but still being controlled by the frontview app control...and it was working great, but Alas, I have to get python 3.7 working in order to do that, and pro ably have to get build-essential working right for that...which I would just like to have back anyway, then I'll be happy camper with current situation as long as the existing apt repos never go away.

Do you know did netgear take down the so called "dev" repo?  that's where their version of build-essential was I believe, I need netgear's version of lib6c-dev in particular.  It seems this repo is no longer up anywhere...the "dev" section anyway...  Maybe I am missing something.  I am getting and ERROR related to netgear's repo in general, so not sure if that is relevant or not..but well..might be beating my head against a wall if netgear took away the actual dev packages such as libc6-dev and build-essential.