So, according to Wiktionary, 感じ is the stem form of the verb 感じる, which used to be 感ずる, which comes from 感 + する with rendaku, where 感 is a Chinese loanword for "feeling".
So Japanese when from 感 (feeling) to 感じ (feeling) by first making it a verb and then turning it back lmao
by Bibbedibob