YouTube has two separate things called tags, and conflating them wastes effort in both places.
Hashtags in the description
These are the ones with the # symbol. You may add up to fifteen, but only the first three appear above your video title as clickable links. Those three are the ones with any real visibility, so treat everything after them as optional filing.
The three should be: your niche, the specific subject, and the format. For a video about camera settings for night photography, that is roughly #photography, #nightphotography and #cameratutorial. Do not waste one on your channel name unless your channel name is something people search.
Video tags in the upload settings
These are the comma-separated keywords behind the scenes. YouTube has publicly downgraded their importance, and they play a minimal role in discovery now. The exception is genuinely useful: they help with common misspellings of specialised terms. If your topic involves a word people routinely get wrong, put the variants there.
Shorts
Shorts behave more like TikTok. Keep tags to about three, make them specific, and match them to what the video actually says. The #shorts tag itself is no longer required for a video to be treated as a Short — the aspect ratio and duration handle that — but including it does no harm.
Where the effort actually belongs
On YouTube, title and thumbnail decide the overwhelming majority of a video's performance. Tags of either kind are a rounding error by comparison. If you have an hour to spend on optimisation, forty-five minutes belong to the title and thumbnail, ten to the description's opening lines, and five to tags.
That is not a reason to skip tags. It is a reason to do them quickly, correctly, and then go do the thing that matters.
The description opening
The first two lines of your description appear in search results and feed into how YouTube understands the video. Writing them as a real sentence about the video — with your key terms in it naturally — does more than any tag configuration.