About downloading file size and WebDAV problems

Downloading file from web interface hasn't the total size of the file

You are downloading a folder. It's a limitation for this case that you can only accept.

Syncing something to server side by NextCloud app always return an error like

You use the word "like". Is the actual error the one you are quoting or not?

I have googled it and I found a temporary solution

You are probably applying a patch which is not designed for an older FileRun version, as there is currently no such problem known to us with the latest FileRun version.

I'm sorry about the word that makes you confused. After posted this question, I have reinstalled all, including os, docker and FileRun, to eliminate variables. The good news is syncing with Nextcloud app works well, however, the problem that size of file not show still happened. Indeed, I am downloading a file instead of a folder, as you can see in the pic above, the file is a pdf.

Sorry, you are indeed downloading a file. Please confirm that the value of your Control Panel setting "Configuration" > "Files" > "Misc options" > "Enable download accelerator" is "None".

Yes, I noticed a post which is similiar with this and you gave the same suggestion in the forum yesterday, and I changed that option from "--select--" to "None", but it doesn't work. In my case, Caddy is in docker as global reverse proxy, the network is attached to host. FileRun is deployed by docker-compose, and the config I am using is based on the official documentation.

EDIT: I fix that aften turned Caddy off and visited FileRun via HTTP, so I guess it's may due to the problem of Caddy or global reverse proxy.

Here is Caddyfile:

DOMAIN {
  tls EMAIL
  gzip
  proxy / localhost:PORT {
    transparent
  }
}

Thanks for sharing the solution!