In reply to Carlos.

Content and functionality are 100% separate from the design aspect when it comes to block themes. This is assuming your theme isn't adding things like custom blocks, which is not allowed at WordPress.org anyway.

The one thing that may be considered "lock-in" is making liberal use of a theme's custom colors, fonts, etc. Because there is no standard naming convention for these under the hood, you could lose the styling on some pages when switching themes. But, your content and functionality do not disappear.