I have focussed my review here on the sections of the paper for which I have decent expertise (notably land carbon fluxes and the remaining carbon budget). My (minor) comments are:

Line 210: What does “forestry” refer to here? I don’t see how forestry (the vast majority of which is deforestation) leads to carbon removal, so mentioning it here seems like it will cause confusion. 

Lines 452-455: In the definition of CDR, it would be worth again mentioning that this definition follows the scientific convention of not including passive carbon sinks. Otherwise, this rather confuses the definition of net zero and its ability to lead to stable global temperatures.

Line 460: I don’t think that transfer of carbon to harvested wood products should count as CDR. This is at best a delayed emission from deforestation. I am glad to see that this flux is not included in the budget (lines 466-468) though the preceding text suggests that they are. For this opening text, I would suggest being more clear at the outset what fluxes are considered to the CDR in the budget (and in the 1.2 GtC/yr number given in the summary). This comment applies also to lines 922-925 which uncritically refers to HWP as a form of CDR. If HWP is to be included in the potential CDR pathways discussed here, I think it is really important to present some evidence that all of the carbon flows involved actually lead to net removal, and under what conditions this is the case. 

Line 1723: Should this be ±220 or a range of 220?

Line 1725-1726: Of course, the authorship of the IPCC chapter and the Forster et al paper is basically the same, so the “backing of the IPCC” seems to evoke some mythical other identity that is a bit of an artifact. I would suggest removing this sentence.

It is an impressive annual update and an increasingly significant body of work. I have some minor comments below to improve readability. On a minor note, the style of the figures is quite different and could be harmonised, but this doesn't detract from the results, discussion and conclusion.

Specific comments:

Line 431 remove “(“ and add comma

Line 627 what are hidden neurons - bootstrapping?

Line 654 summer is not always boreal, also this sentence has something wrong grammatically

Line 659 - missing neurons?

Line 666 and subsequent, shouldn’t xCO2 be written XCO2?? not mole fraction of CO2

Line 1047 this statement seems self-evident something is always greater than nothing

Line 1100 Orphan “(“

Line 1106 “does” should be “do”

line 1176 strange formatting

Line 1212 add “may” underestimate

Line 1247 This sentence doesn’t quite make sense. “As for the ocean…”

Line 1348 should be “is derived from”

Tables: 2 in CO2 should be a subscript