Let's remember that in 2022-23 Trump himself was routinely booed at his own rallies whenever he did two things (and I'll never understand how he ended up so tone-deaf about how passionately his supporters felt about these):
1. He introduced Lindsey Graham, or even just mentioned his name.
2. He bragged about how he made sure COVID vaccines got developed so quickly.
To his credit, he finally gave up on both of these when his 2024 campaign began in earnest.
You are 100% right. He was completely convinced that “operation warp speed” was a bragging point until his own crowds disabused him of that.