If you customized one of the original themes and still used the same directory then those changes would have been most likely copied over.
The best thing to do when customizing a theme:
- If it is just css use the custom.css file
- If you are also modifying a number of templates create a child theme on the theme you are modifying. This way you just include the template files that have changed. See the denim_curve theme for an example (it is a child theme of denim)
There was not many theme changes from Geeklog v2.1.1 to v2.1.2 so if your theme was untouched it should have still worked for the most part (except maybe the block editor). See the docs about half way down the page for the changes:
One of the Geeklog Core Developers.