coppying files to my Iphone to use them off line

If you are using iCloud, this is incredibly easy. On your Mac, press command, shift, 'i'. This will open up iCloud Drive on your computer. Simply copy/paste your files into a folder from within iCloud. Typically, I would use a downloads folder, but really you can use whichever one you want.
It will take a little time, depending on your Internet speed, but once everything has uploaded to iCloud, you can access it immediately on your iPhone through the files app. Simply go to the same folder on the files app on your iPhone, that you uploaded your files to on your Mac, and you will see all of the files. You will have to download them, from iCloud onto your phone, but again that just depends on your data speed.

HTH.

Try using an iOS app called Owlfiles. I've been using it to copy files between my Windows PCs and my iPhone. Owlfiles integrates with the Files app just fine.
The only downside is, you need an ftp client like Filezilla, otherwise you'll be stuck using your browser to upload/download files.
Basically, the way Owlfiles works is you start the built-in servers (free version includes both a http server and a ftp server) and then from your computer you open up Filezilla and put in the IP address, username, password and port shown in Owlfiles and hit connect and once successfully connected you can transfer files between your computer and your iPhone. Not sure if Filezilla is available for Mac though...
Otherwise, if you don't want to rely on a third-party solution, iCloud is probably the best option, especially since you're already using a Mac. I personally tried iCloud on Windows before but it somehow messes up my system restore...

You could also use a USB drive. If you have an iPhone with a USB C port, connect it directly to the phone or use a USB C male to A female adapter if your drive uses a USB A connection. If you have something with Lightning, you'll need Apple's Lightning to USB 3 Camera Adapter and will most likely have to connect a Lightning cable to provide the required power. If you aren't using a Pro iPhone, you'll unfortunately be stuck with USB 2.0 speeds, so it could take a long time if you have many gigabytes of data.
The only other method that might work is file sharing via Finder. Unfortunately, I don't know how this works, and I think it only lets you send files to specific apps.

Localsend is a program I use. It lets you send files or even entire folders via the local network. Depending on the filesize and your network speed that might take a while.

I transfer my local music to my iPhone this way and in works fine. Even though there are a couple unlabled buttons.

Hope that helps.

You shouldn't specifically need FIlezilla. If Owlfiles is setting up an ftp server, any ftp client will work, including the one in terminal, if you comfortable with CLI.

If you want to be able to brows and copy files from your Mac's file and folder structure from your iPhone, you can use file sharing via the Server Message Block (SMB) protocol. To do this:

1. Go to System Settings > General > Sharing, and toggle the "File sharing" switch on.
2. Click the "Show detail" button to the right of the "file sharing" switch, and note your Mac's IP address.
3. In the Files app on your iPhone, double-tap the "More" button near the top right of the screen, and select "connect to server" from the resulting menu.
4. Type your Mac's IP address in the "Server address" field, and double-tap Connect.
5. On the next screen, select "Registered user," type the username and password you use to log into your Mac, and double-tap Next. You should then have access to your Mac's file and folder structure from your iPhone; locate and copy the desired files to your iPhone as if your Mac were an external storage device.
6. When you're done, return to the main screen of the Files app, focus on your Mac, and select the "Eject" rotor action to disconnect it.

HTH

iOS doesn't have an SMB server, so this isn't possible. Remember the system is far more locked down than macOS, so your best bet is using third-party file management apps that can create local servers. Even then, you'll be restricted to viewing the sandboxed environments for those apps.

You also can use copy party, setting up a copy party server is easy, i used claude to do it. :) and install there app on the iPhone. But yes other methods work fine.I just use finder onMac to go to iPhone and in the files tab, paste or drag files into one of the apps folders on iPhone, ftp manager is one app I have.