You said you disabled SIP in Recovery. You did not say you actually tried to delete from Recovery.
rammjet
Try booting into Recovery and use Terminal to rm -rf.
Since Firefox is running Proton, everything you do through Firefox is Proton. Turn off the Proton extension and try again. It should show Mulivad.
Also, to get around the browser situation, try the following command in Terminal. It should be Mulivad:
curl ifconfig.me
Be sure to try it with a rent or mortgage payment.
My personal Invidious server works just fine.
For this application, I like flat files. After the initial sync, I only edit one little md file at a time and syncing it should not take long at all.
Now testing Obsidian -> Remotely Save -> webdav -> Synology NAS
I agree that I don't like the sync stored in a db rather than a directory of files. I just reminded myself that Remotely Save also saves to webdav on my Synology NAS and to Nextcloud. Since I have both available, I will be looking at them again.
I use Obsidian with a docker version of CouchDB. Used to store on Dropbox using Remotely Save.
Ksnip on Linux Mint Cinnamon X11 works great.
Try: sudo chflags nochg the_file
Then try to delete the_file