I found the thread at https://generatepress.com/forums/topic/mobile-menu-break-point-and-header-merge/ and Tom’s snippet works great but I was wondering if there’s a settings option on the dev timeline so the Customizer settings will apply to elements using header merge without needing the snippet (or a checkbox toggle in the header element settings).
One additional issue I discovered is when using the snippet, the custom logo indicated in the header element settings isn’t applied. When you visit https://victorygardens.org/event/tiny-beautiful-things/ on desktop, you’ll see the white text in the logo (this is the custom logo via header element settings), but on tablet it reverts to the default logo (black text).
Good deal on the 1.9 update and needing the mobile logo was the answer. I didn’t make the connection that the mobile version would be needed in that instance but it makes sense after you pointing it out and looking at the snippet again.