Charlie-Ramirez-Animation-Studios-de-MX
commented
2 years ago Ubuntu 21.10 is still beta (at this time) Actually it is normal that it cannot find the directory for the version. (that's why the error that throws you as 404/ "does not have a Release file.")
[I have debian so I can't test it directly but] You could try installing it via synaptic's package manager. If you have a graphical interface, you can simply search for it in the store or through sudo apt-get install synaptic (although the repository version may be installed)
Another option is that you could temporarily install it using the .deb file for the stable of ubuntu (Hipo) SSR version 0.4.2-2 https://www.ubuntuupdates.org/package/core/hirsute/universe/base/simplescreenrecorder
it is supposed to work the same at least until the repository for 21.10 is created
sudo apt-get update && sudo apt-get dist-upgrade Ign:1 http://ppa.launchpad.net/maarten-baert/simplescreenrecorder/ubuntu impish InRelease Hit:2 http://kali.download/kali kali-rolling InRelease
Err:3 http://ppa.launchpad.net/maarten-baert/simplescreenrecorder/ubuntu impish Release 404 Not Found [IP: 2001:67c:1560:8098::19 80] Reading package lists... Done E: The repository 'http://ppa.launchpad.net/maarten-baert/simplescreenrecorder/ubuntu impish 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.