I would not go to any party that BM threw, nor would DH. And especially not in the middle of a pandemic.

We hosted graduation parties, showers and weddings and invited BM and her DH.  I didn't see any way out of it.  I dreaded each occasion and put an incredible amount of work, sweat and tears into making sure I looked my very best.  Now that both she and her DH are dead. I look back and wonder why I was so insecure.  She should have been kissing my feet for raiding her 3 kids.

Does not mean playing nice to BM.  Just throw a party by yourself for SK.  Rent a cabin somewhere safe or something 

My DH would not go to anything his ex was hosting. 

DH admitted to me he doesn't want to go because of Covid and he is uncomfortable around her

Then, he should not go. He can do something with/for his daughter on his own.

My DH will not be in the same room with BM so he would not go, Covid or no Covid. He had enough of that bitch when he was married to her.

We had separate parties and events for the step-kids and events together for my son with my ex and his family.  Simple reason is BM is toxic in our situation. Always causing issues, harassing us etc. 

The only events that we ever attended together were public graduation ceremonies where we sat a football stadium apart and a step-kids wedding where again we were seated far apart.  Events such as showers as things I send gifts and don't go.  My DH doesn't go to anything for the kids.  He unfortunately had to even stop going to school events their last few years of school because of BM's toxic behavior. For stepsons graduation from college, she invtied DH only to a dinner after graduation.  He of course did not go and did not even respond.  

Stepkids are grown now but unless a situation is friendly I think it best not to go.  

"In the beginning" when Toxic Troll was somewhat civil and we hadnt gone through what we have gone through, Munchkin would have pool parties at BM apartment complex and we would show up, sit on the sidelines and drink our cocktail of choice. Provide snacks and pizza and cake.

NOW, SD is older, and we do things separately. ALWAYS. When SD Feral Forger graduated we sat on completely separate sides of the field.

COVID safety should give the perfect out. Celebrate separately.

Oh hell no. We would never go to anything hosted by BM and if my DH even considered, he can pack his bags.

we do our own separate everything.

My philosophy has always been "separate is best." If your DH wants to celebrate SK graduation, then do your own party. (COVID safe, of course). 

I'm lucky - my SO and his ex do not speak, nor does SD, so BM is out of the picture completely.  

I did attend SD's college graduation when I was still trying with her.  Now I would support SO going but would not attend.  Since SD is basically a loser I don't expect many significant celebrations forthcoming anyway.  SD wants to have surgery to look male and wants a hysterectomy, and has apparently been running around trying to sell her eggs to fertility clinics before that happens.  Those eggs should have a big warning label attached to them, but it is no concern of mine - but it means no grandkids for SD to weaponize either.

We never did anything with the blended family opposition (the SpermClan).  Not a thing. Ever, not once in the 16+ years of my SS's Custody/Visitation/Support CO.

They never made any effort to participate in ny milestones for my SS.  Not even a card for his HS graduation, or his USAF BMT graduation.  No attempt to participate though they were invited.  That we never lived nearer than 1200 miles from SpermLand and SS had 7wks of vistation per year (5wks summer, 1wk winter, 1wk spring) which the SpermClan periodically waived for a year or more over the years, probably influenced their choices to not participate.  SS never got a graduation announcement for any of his three younger also out wedlock Spermidiot spawned half sibs.  That side of family never made an effort to engage with him, or to include him beyond the periodic visitation that they did take.  Never without drama, never without their manipulation, and never without trying to load my SS up with their toxic bullshit.

That said, if my DW was invited, I would be right there with her, invited or not.  I would not tolerate the blended family opposition pulling any shit, we would be there together at our sons side, to celebrate him and minimize their toxic crap.