Get Taxonomy Term ID by Node in Drupal 8 & 9
If you want to get Taxonomy Term data you can use this code:
Hope it will be useful for you.
PS: If you need just Term's id you can use this:
You will get something like this:
[0 => ['target_id' => 23], 1 => ['target_id'] => 25]
In example my field has 2 referenced taxonomy terms. Thanks!