Why am I getting charged for these, & what are they exactly?
Unless you are on a support contract this is part of the ongoing maintenance required to keep your website running smoothly & to keep it secure.
Hang on, shouldn’t this be included in my hosting charges?
Most of the time, minor, incremental updates to WordPress Core are free of charge. However, for major versions, or updates with fundamental code changes which may cause problems, I charge for the time I spend running those updates & checking compatibility. WordPress 5.6/5.7 made significant changes that caused many sites to break.
What about theme and/or plugin updates?
Again, this depends on the theme or plugin & whether or not there is a time commitment that is significant enough to warrant a charge. An example of a plugin that fits this category is Woocommerce.
Examples of themes that fits this category: Uncode, Avada, Salient (or any other everything but the kitchen sink style theme).
A custom theme, one developed by a third party or one I have inherited also tick the boxes.