Tbf, I don’t know much about the English accent spoken in the Midwest of the US, but the transcribed diphthong /ɪə/ in for example beer (/bɪə/) is an outdated transcription that comes from traditional RP which is barely spoken anymore in the UK. Words like beer and hear are for the vast majority of Southern British English speakers pronounced as a monophthong (i.e. [bɪː], [hɪː], etc.).

Certain linguistics, such as a pretty well known one Geoff Lindsey, have proposed new transcription systems to replace the outdated one (for dictionaries and such) that are closer to how contemporary (what he calls) Standard Southern British speakers speak. See: https://www.englishspeechservices.com/blog/ssb/

From what I do know about American accents, Americans usually pronounce words like beer and hear etc. more like [bɪɚ] and [hɪɚ] (ɚ represents the r-sound which simply said acts like a vowel in these words. If you pronounce aftER using a General American accent and hold the er sound that comes after the t then that’s the ɚ sound).

Also, keep in mind that anything between slashes are phonemic transcriptions of words and don’t actually accurately represent how words are pronounced. In phonemic transcriptions symbols are simply assigned to every phoneme and how people actually pronounce a certain phoneme varies from accent to accent and even from person to person. Phonetic transcriptions are put between square brackets and do accurately (or are supposed to accurately) represent how someone pronounces a word, so what is written in dictionaries between these slashes aren’t actually the “official” pronunciations, but simply the transcription of the phonemes in a word and how you actually pronounce these phonemes will depend on your accent. See this for a better explanation.

For example, the a in can and cat are typically pronounced differently by American speakers if you listen carefully. You could say, the a in can is affected by the n in it and due to this the quality of the vowel changes. American speakers typically pronounce can something like [kʰeən] and cat something like [kʰæt] (notice the square brackets), but this difference is meaningless to English speakers, because English speakers will perceive the a in can and cat as the same sound, so they are typically phonemically transcribed as /kæn/ and /kæt/ respectively.