I've had this issue as long as I can remember, since I switched from firefox to edge (around v91). Edge pdf reader has horizontal visual artefacts that make individual lines of text sometimes almost impossible to read. I cannot replicate this behaviour with other browsers, so it seems to be something to do with the edge pdf reader itself. This happens with all pdf files opened with edge. Below is an attached image of what this looks like. Currently using Version 97.0.1072.69 on Windows 10.
You can make this effect go away, or make it to move to some other part of the pdf, by toggling on-off the pinning of the pdf top bar (which has search, zoom etc.). Might help finding the cause.