The red stamps are the official stamp of the temple, similar to a signature. Often these will use an old or unique way of writing the kanji. Also the Japanese kanji is from China so there are lots of similarities to Chinese Simplified and Chinese Traditional. You should definitely visit if you can and take a Shodo class.
Damn I realize I need to do a deep dive into Asian languages history 👀
So I can develop my own stamp of my “inner temple”?
Yes! You can personalize your own印鑑 stamp with whatever design. Depending on the material and where you get it done it will cost between $30~$500 usd.