What is "Temple Judaism" and how does it differ from modern day Judaism?

Hi all,

Hope you are all doing well.

Talking to different Christians (especially Catholics) and reading over their subreddits, there seems to be this idea that modern day Judaism is radically different and has almost no relation or connection to “Temple Judaism.” This is almost always used to back up and defend Christianity as the one true faith (which is sort of ridiculous since all Christian denominations have changed quite considerably since their inception).

I’m fairly ignorant on this subject so I would appreciate a little explanation. Some commentators have even argued that modern day Judaism is essentially a different faith and has no connection. I don’t trust these people (for a variety of reasons) but I’m interested in exploring the ancient roots of Judaism and how it’s changed.