After downloading TCOE, I am trying to make an artificer, but many items are no longer showing up, when I search for them (scimitar, double scimitar, longsword, short sword, pike …). Additionally, some items are not being factored into AC and saving throws (e.g. cloak of protection). These are still working for my other characters. Could this be a coding issue, or is there some rule about artificers I’m not aware of?

Artificers are only proficient with simple weapons, so none of the ones you listed. And a cloak of protection has to be attuned for it to work.