I definitely wouldn't undo the work that was done to get rid of the original antenna mount. Perhaps something like this would work for you: https://smile.amazon.com/dp/B07R7RCRW9/ I don't have any experience with this particular one (I don't use am/fm, it's all commercials these days) but there seem to be a lot of good reviews.
anything like this could work, you might even be able to run the cable through a window and get the antenna outside ?
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But it doesn't happen for aux input, car play, or anything else?
Sounds like the antenna or antenna adapter or wiring to the antenna..
You could buy one of these and try installing it into the radio to see if its actually the antenna... might be a good troubleshooting idea.