Playing at Level 20?

[S'mon]

The biggest thing I've noticed at the highest levels is that it is actually easy to build an encounter that kills PC's.

I've noticed that just a few giants can do obscene amount of damage even to PCs with a decent AC. My son attacked 3 fire giants with his dragonborn Bbn-19 expecting an easy fight, and got a major ass-whupping

 

[Tormyr]

I was wondering how often do GMs give out Epic Boons?
When I had an individual PC hit 20 in my sandbox Wilderlands game, he got EBs for:

1. At BBn-19 he soloed Kainos Warbringer, a CR 25 demigod son of Ares-Bane - hit BBn-20 and my son persuaded me it was so outrageous the PC (not his) should get an EB too.
2. Finally killing Borritt Crowfinger, the (recently turned Lich, CR 21 + minions) BBEG Prince of the Black Sun who'd been the main villain for 7 years of play.
3. Soloing Matriarx, a CR 21 ancient black dragon - though that was a bit of a kerbstomp battle.

I've been looking at how I should give out EBs in my Runelords campaign with a bunch of PCs at 20th likely long before the finale. Soloing a CR 21+, and completing a major quest, seem like two possibilities. I'm not very keen on tracking XP-for-boons, it feels like it should need something, well, 'Epic'.

In my 5e Age of Worms campaign, I had the heroes attain 20th level halfway through chapter 11. When they finished chapter 11, they gained an epic boon as a sort of "level 21" before starting the final chapter.