The reply from @andyross ended up solving my problem.
Instead of randomly switching resolutions, which was my earlier approach, I systematically switched resolutions, working my way from the lowest to the highest. Specifically, I first switched the Roku display setting to the lowest possible resolution (720p) and then systematically increased the resolution one step at a time until I reached 4K HDR 30 fps, which is the limit of my TV. Since then, fonts have been displaying normally.
Thanks go out to @andyross . I hope this helps you too.
This issue still needs to be fixed. My text keeps changing back to being blurry. Sometimes it's fine for a couple of days and sometimes it's only a few hours until the text reverts back to being blurry. A work-around isn't a fix.
Roku released an update a few days ago with that being one of the possible fixes. It is 12.0-4181 or something like that. You can go to the update check in system settings if the about screen doesn't show it updated yet