Can't install Keyman in Ubuntu 18.04.3 (on laptop)

I am finding that I can’t install Keyman 11 in Ubuntu 18.04.3. I am using:
sudo add-apt-repository ppa:keymanapp/keyman
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install keyman onboard

I get pages of printout which include a notice:
No-pubkey 76F1A20FF987672F. What does this mean and what can I do about it? Any help is greatly appreciated. I’d like to review some Russian and Classical Greek which I learned in college and could really use Keyman.

I think that error involves the wine PPA, not Keyman.

See https://askubuntu.com/questions/1103240/signature-verification-error-for-wine-index-files-failed-to-download-changin?noredirect=1&lq=1

The thread suggests getting a new key

wget -nc https://dl.winehq.org/wine-builds/winehq.key && sudo apt-key add winehq.key && sudo apt update

The above worked perfectly and solved that problem. Now when I type in sudo add-get-repository ppa:keymanapp/keyman I get the response that the release file Not found [Ip:2606:4700:10::6814:5f72 80] (error 404)
Then a few lines farther down --------------------- $ Release does not have a release file. And "Updating from such repository can’t be done securely and is therefore disabled by default.
Any help you can give will be greatly appreciated. What hoops do I have to jump through to find this release file which is missing. I believe that others have got Keyman to run in ubuntu. How did they do it?
I can’t use a link in a post due to the computer telling me that a new user can’t use a link. I am not going to give up on this. I loaded Keyman 8 a few years ago and it never did work either.

Now when I type in

sudo add-get-repository ppa:keymanapp/keyman

Sorry you’re still having difficulties installing. That looks slightly different from the install steps from https://keyman.com/linux/ .The install steps for Ubuntu users is just pasting the following into a terminal:

sudo add-apt-repository ppa:keymanapp/keyman
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install keyman onboard

I can’t use a link in a post

I’ve updated your user permissions so you should be able to include a link now.

Sorry for the careless error. I think I may have to let some time pass and RTFM for a while. The first command tells me: “E: The repository ‘http://packages.sil.org/ubuntu $ Release’ does not have a Release file. N: Updating from such a repository can’t be done securely, and is therefore disabled by default.” The second command repeats the message. The 4th command says that keyman and onboard are already the newest version. Keyman still won’t run. I worked in electronics many years and I know that a failure is often from some stupidly simple cause. This probably is too.