Is it possible to run multiple versions of MySQL Workbench? I'm doing an application migration from MySQL 5.5 to workbench v8... 5.5 supports MySQL Workbench up to version 6.3... However, MySQL server 5.5 only supports up to version 6.3 of the workbench.

I have an instance of MySQL server 8.0 on the same machine also that I need to manage.  Is it possible to have two different versions of MySQL Workbench installed on a Windows 10 dev machine at the same time?
I don't see why not. Are you encountering errors installing two versions at once if you specify different install paths? You may have to use different versions of the MySQL installer as well.

It does look like Workbench 8 is compatible MySQL 5.5, though (and I can confirm because I have been using it). The documentation says some queries will not work like showing the processlist (although I just tested this and I can SHOW FULL PROCESSLIST of my MySQL 5.5 server with MySQL workbench 8.0.12.)