How to install a newer version of MySQL workbench than is available in my distro's repos

It does not seem that Debian's APT reposistories have the newer version of MySQL. And since you want it maintained by APT, rather than install from source code, you can use MySQL's official reposistory. There is a deb package for APT installation here, with short instructions

First, add the MySQL APT repository to your system's software repository list. Follow these steps:

Go to the download page for the MySQL APT repository at http://dev.mysql.com/downloads/repo/apt/.

Select and download the release package for your platform.

Install the downloaded release package with the following command, replacing version-specific-package-name with the name of the downloaded package (preceded by its path, if you are not running the command inside the folder where the package is):

shell> sudo dpkg -i /PATH/version-specific-package-name.deb

For example, for version w.x.y-z of the package, the command is:

shell> sudo dpkg -i mysql-apt-config_w.x.y-z_all.deb

Note that the same package works on all supported Debian and Ubuntu platforms.

During the installation of the package, you will be asked to choose the versions of the MySQL server and other components (for example, the MySQL Workbench) that you want to install. If you are not sure which version to choose, do not change the default options selected for you. You can also choose none if you do not want a particular component to be installed. After making the choices for all components, choose Apply to finish the configuration and installation of the release package.

You can always change your choices for the versions later; see Selecting a Major Release Version for instructions.

Update package information from the MySQL APT repository with the following command (this step is mandatory):

Then install normally using sudo apt-get install mysql-workbench

I don't know if you found the solution or not. There are several options you could try out -

1. Upgrade from jessie to stretch and get 6.3.8+dfsg-1

2. File a wishlist bug saying you would like mysql-workbench to be backported to jessie. See https://itsfoss.com/bug-report-debian/ if you want to learn how to file a bug.

3. Use one of the options above.

The rest, as they say is upto you.

First check the version of your OS, if it is: Ubuntu 20.04 then download Ubuntu Linux 20.04 (x86, 64-bit), DEB Package from https://dev.mysql.com/downloads/workbench/

Be careful with the version of OS and your downloaded Workbench version

Then open a terminal and follow these commands:

1. cd Downloads (if the file is in the Download folder)
2. ls (copy the file name)
3. sudo apt install ./filename (e.g. sudo apt install ./mysql-workbench-community_8.0.22-1ubuntuversion no_amd64.deb)

I am on Ubuntu 20.10 now. That's what has worked to me:

1. Download MySQL APT Repository from https://dev.mysql.com/downloads/repo/apt/ as mentioned by @john-k
2. sudo dpkg -i mysql-apt-config_0.8.16-1_all.deb, again, as John said.
3. sudo apt-get install mysql-workbench - this did not work to me so you may skipp it too. I got the following error:

...
Package mysql-workbench is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
  mysql-workbench-community

E: Package 'mysql-workbench' has no installation candidate

4. sudo apt-get install mysql-workbench-community - this worked, weirdly. Got this notification back:

...
mysql-workbench-community is already the newest version (8.0.18-1ubuntu19.10).
The following packages were automatically installed and are no longer required:
  adobe-flash-properties-gtk libcaf-openmpi-3 libcdio18 libcfitsio8
  libdns-export1109 libdvdread7 libevent-extra-2.1-7 libffi7:i386
  libgeos-3.8.0 libgfortran-9-dev libgrantlee-textdocument5 libgsoap-2.8.91
  libicu66:i386 libllvm10 libllvm10:i386 libmalcontent-0-0 libmozjs-68-0
  libmutter-6-0 libnettle7 libnettle7:i386 libpoppler97 libproj15 libqpdf26
  libsane libsrt1 libtepl-4-0 liburl-dispatcher1 libx264-155 libx265-179
  openmpi-bin openmpi-common
Use 'sudo apt autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 2 not upgraded.

5. sudo apt autoremove - clean up has been recommended, so I did it
6. sudo apt-get update - resynchronize index files from their sources.
7. sudo apt-get install mysql-workbench-community - this finally installed it.
8. mysql-workbench --version results to the following now:

Found /usr/lib/x86_64-linux-gnu/libproj.so.19
MySQL Workbench CE (GPL) 8.0.23 CE build 365764

For beginners who land here from google on Ubuntu and may not necessarily have a strict need to use sudo apt-get mysql-workbench but are more familiar with it than manually downloading packages… using apt-get is not the only option!

1. Simply uninstall the older version of mysql-workbench that comes with your distro (presumably you've done that and now realize the version is too old):

   sudo apt-get remove mysql-workbench
   

2. Go to https://dev.mysql.com/downloads/workbench/ (don't bother registering).

   Download the package and double click the downloaded package, software center takes over.

3. Access it via finder to connect to your remote databases type "mysq".