Posting a YouTube video on Instagram can be a bit tricky because Instagram doesn't allow you to upload a YouTube video directly to your account. However, you can still share the video with your followers by following these steps:
Open the YouTube video you want to share on Instagram.
Click the "Share" button below the video.
Click the "Copy" button to copy the link to the video.
Open Instagram on your mobile device and tap the "+" icon at the bottom of the screen to create a new post.
Select the video icon at the bottom of the screen to choose a video from your camera roll.
Select the video you want to post from your camera roll. You can also trim the video if needed.
Tap "Next" and then "Share" to post the video on your Instagram account.
Alternatively, you can also use third-party apps or websites that allow you to download YouTube videos and then upload them to Instagram. However, keep in mind that downloading and reposting someone else's content without permission may violate copyright laws.