Viewporting is a rather fundamental aspect of the way the library is designed (much of the complexity analysis in the implementation depends on it) and not something that can be turned off. (I keep getting CM5 support requests where people set viewportMargin: Infinity and then are surprised when the editor gets slow. I want to avoid that failure case this time.)
The way this breaks browser search is very annoying, but a trade-off that seems unavoidable with this design.
A repro case for viewport bugs would be very useful. Your issue might have been solved by @codemirror/view 0.19.9, which makes this more robust.
Browser plugins that just jump into pages and start messing with editable DOM are, from the perspective of an editor maintainer, a really terrible idea and not something I’m very sympathetic to.