1
Open Safari
The in-app browser inside TikTok, Instagram or X often blocks downloads. Copy the link, then switch to Safari.
2
save4social.com
Paste the link, press Download, wait out the short ad, then tap the MP4 row.
3
Files
When it finishes you get the share sheet or the file in the Files app. It does not appear in Photos by itself.
Permission
If Safari asks to allow downloads, allow it. Private tabs work too; the file still goes to Files.