To save Twitter videos without watermarks to your iPhone or iPad, you can use TwitClipper. The steps vary depending on the OS version:
You can download using the Safari browser.
First, open the Twitter app and tap the "Share" button.
Tap the "Copy link" button to copy the video link.
Access TwitClipper on the Safari browser of your iPhone or iPad.
Paste the video link into the search box. Right-click the input box and tap the "Paste" button.
Tap the "Search" button.
Click the "Format" and "Download" buttons to save the video or audio.
Click the "Download" button in the popup dialog.
When the video download starts, a download icon will appear in the top right corner of the browser. Tap it to open the download list. There you'll find the thumbnail of the desired video. Tap it.
Long-press the desired video and select the "Share" button.
Select the "Save Video" option from the popup menu to save it to your gallery.
Congratulations! Your video is ready to play.