The first holidays arrive whether you're ready or not, and everyone will have opinions about what you "need" - company, tradition, distraction, family. Here is the actual rule: there is no rule. There are three complete plans.
Plan A: showing up
Go to the dinner. Let it be strange. Their absence will sit at the table like a guest, and that's not a failure of the day - it's honest. Tell one person beforehand: "If I leave the room, I'm fine, I just need a minute." That one sentence buys you every exit you'll need.
Plan B: showing up briefly
One hour. Coat stays near the door. You come for the toast or the meal or the kids opening presents, then you go home to your own quiet. Anyone who loves you will understand; anyone who doesn't understand has told you something useful about them.
Plan C: not showing up
A day alone with takeaway and a film is a complete plan. So is booking a trip and being somewhere with no traditions at all. Skipping the day doesn't dishonor them. The calendar is not the boss of your grief.
Pick one plan and reserve the right to switch to another at any point, including mid-meal. All three are complete. All three count.