Custom Fields are missing/ not functioning properly

I have a problem here on a clients event site:

A month before it worked great: the selection of the location for event calendar via Jevents Custom Fields.
Since last week it doesn't work anymore.

At first I thought it would help to take the steps that gave me error messages directly (adjust PHP version and adjust Max_Input_Vars) The errors went away, but still doesn't work properly.
The plugin would be mainly JEvents Custom Fields - would as I see it also be up to date.
I noticed that the fields in the backend are also missing:

1 year ago, Actual working Field Inputs : Image 1
Now, it doesn't show me any Field Inputs: Image 2
Frontend, but the Options still remain and partially work: Image3


Here are the Support infos:

PHP Version : 8.0.25

MySQL Version : 10.3.36-MariaDB-log

Server Information : FreeBSD s41.server.hostpoint.ch 12.3-RELEASE-p6 FreeBSD 12.3-RELEASE-p6 releng/12.3-n234208-bc1774dd115 HOSTPOINT amd64

Fix jQuery? : Yes

Load JEvents Bootstrap CSS? : Yes

Max Input Vars ? : 3000

Club code set? : Yes  

User Agent : Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/106.0.0.0 Safari/537.36  

Joomla : 3.10.11

component_com_jevents : 3.6.43

component_com_jce : 2.9.32

module_mod_jevents_cal : 3.6.43

module_mod_jevents_custom : 3.6.43

module_mod_jevents_filter : 3.6.43

module_mod_jevents_latest : 3.6.43

module_mod_jevents_legend : 3.6.43

module_mod_jevents_switchview : 3.6.43

layout_JEventsFlatplusLayout : 3.6.6

plugin_2021-04-09-old-jevents_jevanonuser : 3.6.0 (not enabled)

plugin_2021-04-09-old-jevents_jevcustomfields : 3.6.3 (not enabled)

plugin_actionlog_jevents : 3.6.43

plugin_content_jevents : 3.6.43

plugin_finder_jevents : 3.6.43

plugin_installer_jeventsinstaller : 3.6.43

plugin_jevents_jevanonuser : 3.5.5

plugin_jevents_jevcustomfields : 3.7.6

plugin_search_eventsearch : 3.6.43

plugin_system_gwejson : 3.6.43

I hope someone can help me with this.
My knowledge of joomla is rather shallow.

Thanks in Advance!
If you wanna inspect the Website its https://www.wangenbo.ch/veranstaltung-hinzufuegen


TIA