With the risk that Twitter doesn't do justice to the story, I'll take a stab at it anyway.
Firstly, let me say that it's primarily about Boot, not the Spring Framework itself.

The biggest issue I have with it, is that it is focusing on writing less code. Not better code. (1/7) https://twitter.com/wimdeblauwe/status/1312099960465227776

Developers get carried away with the magic it offers and forget about basic design principles.

Also it tends to be intrusive. When using Spring Boot, you're practically married with it. A clean architecture with the framework only on the outer rim is possible, but hard. (2/7)

Another big annoyance is the vast amount of dependencies that gets carried in.

@BrianVerm did a nice experiment on this:
https://twitter.com/BrianVerm/status/1276175013327056896?s=19

I notice many of my peers have no idea what weight they're carrying in with adding yet another convenient starter pom. (3/7)

Then there's the big dependency on deep reflection and bytecode manipulation. It makes debugging problems with the framework extremely hard.
That may not happen all too often, but when it does, it hits you hard. With days of lost productivity. (4/7)

Lastly, a (maybe slightly esoteric) annoyance for me is that the aforementioned points make it very hard to use Java modules.
I did this on a project and for a conference talk.

(5/7)

At first it seemed OK, until I decided to upgrade from Spring Boot 2.1 to 2.3 for the new conference season.
That solved some of my earlier problems, but introduced new ones that were even harder to crack.
(6/7)

To sum it all up:
It may speed up your development at the beginning, but it slows you down in the long run, because it is an open invite to sloppiness. (7/7)