TOPIC:

It's a simple site I run for my american legion post. I only create events on the admin part of the site, not on the public available side. After the joomla and jem version update I haven't been able to edit or create events and just tried to create a new category and get the same issue. I can create/edit venues.

I think there was a problem on updating. Did you try to install both, joomla and jem update, again?
What I think is that the url generation could be broken, because the correct url could be:instead ofEventually this could be a problem, but I am not shure.

But I have no more ideas, sorry.

The problem I'm talking about occurs in the backend when you go to Components -> JEM -> Event and try to create a new event or edit an existing event or to edit or create a category

I have downloaded joomla 3.9.2 and reinstalled it and downloaded jem again and reinstalled it as well.

That's really strange. Because you are saying nothing about your system (template, additional plugins etc. I think you are trying on a clear JEM 2.2.3 on a clear Joomla! 3.9.2 with protostar. With that you shouldn't have problems. I don't have problems.
If you are not on clear Joomla! and JEM, then you should give more informations. Mostly there are some additional plugins or templates which causes such problems. Buth without any informations, we can't and won't help.

The site worked fine with everything installed until both the site and your software update.
Site template is: Kirigami v1.12 RocketTheme Joomla Template Club I use this exact template, jem on several other sites and they work fine together.

other than the joomla files, this is what is installed on the site:

Components:
RokCandy
RokGallery
RokSprocket
JEM
Gantry 5 Themes
File:
Gantry 5 Nucleus Engine

Libraries:
Gantry 5 Framework
RokCommon
Gantry 4 Framework

Modules:
JEM - Module-Calendar
JEM - Module-Basic
JEM - Module-Wide
JEM - Module-Banner
JEM - Module-Jubilee
Gantry 5 Particle
RokWeather
RokSprocket Module
RokNavMenu
RokMiniEvents3
RokGallery Module

Package
RokBox Package
JEM - Package
RokSprocket Package
RokGallery Package
RokCommon Package
Gantry 5

Plugin
RokPad
Content - RokInjectModule
System - RokSprocket
System - RokCommon
Button - RokComments
Content - RokComments
System - RokCandy
Button - RokCandy
Button - RokBox
RokBox
System- Gantry 4
Gantry 5 - Presets
Quick Icon - Gantry 5
System - Gantry 5
JEM - Mailer Plugin
JEM - Comments Plugin
SMart Search - JEM
Search - JEM
Content - JEM
System - RokBox