let me rewrite your network drawing -might be like this?
both relevant applications are behind your Caddy reverse proxy.
CODE editing process starts number of requests you be seeing in your logs:
This requests must be visible in Caddy, Nextcloud and CODE - sometimes you must adjust proxy settings to show access logs but as this is the most central part I would start there. the logs above are simplified but you easily spot them.. check and post the logs showing this requests.Browser console could show you something as well.
Update: here is a snippet from my reverse proxy log:
"2025-02-17T07:30:06+01:00","192.168.11.203",200,"dev-nc.mydomain.tld","/apps/files/api/v1/views","dev-nc@docker",200
"2025-02-17T07:30:06+01:00","192.168.11.203",207,"dev-nc.mydomain.tld","/remote.php/dav/files/willi/federation_share/office%20doc%20in%20a%20federated%20share%20folder.odt","dev-nc@docker",207
"2025-02-17T07:30:06+01:00","192.168.11.203",200,"dev-nc.mydomain.tld","/apps/files/api/v1/views","dev-nc@docker",200
"2025-02-17T07:30:06+01:00","192.168.11.203",200,"dev-nc.mydomain.tld","/apps/richdocuments/token","dev-nc@docker",200
"2025-02-17T07:30:06+01:00","192.168.11.203",207,"dev-nc.mydomain.tld","/remote.php/dav/files/willi/federation_share/office%20doc%20in%20a%20federated%20share%20folder.odt/","dev-nc@docker",207
"2025-02-17T07:30:06+01:00","192.168.11.203",200,"collabora.mydomain.tld","/browser/9f2e55c/cool.html?WOPISrc=https%3A%2F%2Fdev-nc.mydomain.tld%2Findex.php%2Fapps%2Frichdocuments%2Fwopi%2Ffiles%2F138149_oc52dthqts8g&lang=en&closebutton=1&revisionhistory=1","collabora@docker",200
"2025-02-17T07:30:06+01:00","fd00:feed:beef:1::6",200,"dev-nc.mydomain.tld","/index.php/apps/richdocuments/wopi/files/138149_oc52dthqts8g?access_token=kxD30Q68IeFTY9TdGRJylvl1xeT2oOSa&access_token_ttl=0","dev-nc@docker",200
"2025-02-17T07:30:06+01:00","fd00:feed:beef:1::6",200,"dev-nc.mydomain.tld","/index.php/apps/richdocuments/wopi/files/138149_oc52dthqts8g/contents?access_token=kxD30Q68IeFTY9TdGRJylvl1xeT2oOSa&access_token_ttl=0","dev-nc@docker",200
"2025-02-17T07:30:07+01:00","192.168.11.203",200,"dev-nc.mydomain.tld","/index.php/apps/files/preview-service-worker.js","dev-nc@docker",200
"2025-02-17T07:30:07+01:00","192.168.11.203",200,"collabora.mydomain.tld","/browser/9f2e55c/nextcloud/images/scroll-double-dark.svg","collabora@docker",200
192.168.11.203 - is the client
fd00:feed:beef:1::6 - CODE container accessing the NC