Commander Legends: Battle for Baldur's Gate is an extra-large set with 141 commons, 120 uncommons (30 of which are legendary creatures), 77 rares (25 of which are legendary creatures), 22 mythic rares (5 of which are legendary creatures or planeswalkers that can be your commander), and one card of special rarity (Faceless One).
Draft boosters of Baldur's Gate have 20 cards (and an additional ad card). Draft booster boxes have 24 packs. Each draft booster has a background card, at least one legendary creature (or planeswalker that can be your commander), and a foil card. Draft boosters are printed in Belgium.
The Belgian printing uses sequential collation.
Packs are front-facing and start with 13 commons. Then, there are 2-3 non-legendary uncommons. Next are the legendary creatures, planeswalkers, and backgrounds. Uncommon and mythic legendaries come first, then backgrounds, then rare legendaries. There is always one background, but there can be 1-2 legendaries. There can be two uncommon legendaries; there can be a rare legendary with or without an uncommon legendary; or there can be a mythic legendary which (probably) cannot be in the same pack as another legendary. The background card can be of any rarity independent of the other legendaries. After these cards is a rare (that is not a legendary creature or planeswalker), a foil, and then an ad card. If Faceless One appears, it will appear as the last common. (If it is possible to get more than one (non-foil) rare and/or mythic rare legendary creature and/or planeswalker, I haven't observed it.)
|13 Commons||3 Uncommons||1 U. Legendary||1 Background||1 Rare||1 Foil||1 Ad Card|
|13 Commons||3 Uncommons||1 Background||1 R. Legendary||1 Rare||1 Foil||1 Ad Card|
|13 Commons||3 Uncommons||1 M. Legendary||1 Background||1 Rare||1 Foil||1 Ad Card|
|13 Commons||2 U.||2 U. Legendary||1 Background||1 Rare||1 Foil||1 Ad Card|
|13 Commons||2 U.||1 U. Legendary||1 Background||1 R. Legendary||1 Rare||1 Foil||1 Ad Card|
There are three common runs. Both the A and C runs have 60 different cards (each appearing twice) plus one copy of a shared 61st card, Heap Gate. The B run has 15 different cards (each appearing eight times). Each pack contains 5-6 A cards followed by 1-2 B cards and 5-6 C cards. Additionally, packs will have 0-1 copies of Faceless One which acts like a D common run (although this card is probably not the same rarity as actual commons). Faceless One probably occurs in about 1/6 of packs (matching the assumed rarity of The Prismatic Piper in the original Commander Legends set). I have not recorded Faceless One in a pack with 2 B commons. Assuming these things hold and assuming symmetry between A and C (empirically plausible), then, mathematically, assuming common cards from different runs have equal rarities, in packs without Faceless One, 5 A packs should appear 663/2570 of the time, 1 B packs should appear 622/1285 of the time, and 5 C packs should appear 663/2570 of the time.
Commons with showcase treatments appear in the B run wherein 2 out of 8 copies are the showcase version.
There are two non-legendary uncommon runs. The A run has 60 different cards (each appearing twice) and the B run has 15 different cards (probably each appearing eight times). Each packs has 2-3 cards from A and B together which breaks down as 2-3 A cards followed by 0-1 B cards. The exact breakdown of cards in these slots is also interdependent with what happens in the legendary slots, so it can be complicated, but the empirical rate of 3 A packs is very low (31 observed out of 30 boxes), and it seems empirically plausible that uncommons from A and B have the same rarity (which means that B cards appear at a rate slightly above 1/2). Cards with showcase treatments appear here in the B run wherein (probably) 2 out of the 8 copies are the showcase version.
There is one run of legendary (non-background) uncommons. There are 30 cards in this run (with each appearing four times). Pack get 1-2 cards from this one (as part of 1-2 total legendary creatures and/or planeswalkers). It seems empirically implausible that these uncommons have the same rarity as non-legendary uncommons; probably their as-fan is a bit higher. The chance of a rare or mythic rare legendary creature or planeswalker is given by Wizards as 31%  (closely matching my empirical observation of 224/720 with 19 being mythic rare). Even with knowledge of this rate and a characterization of the non-legendary uncommons, there is still a gap to understanding the distribution of these cards because of correlations of the rarities of the legendary cards with the non-legendary runs. Mythic rare legendary creatures and planeswalkers seem to only appear in packs with a B uncommon. Rare legendary creatures can appear in all pack types (with a B uncommon, with 3 A uncommons, or with a legendary uncommon), so perhaps there is no correlation in this case.
|A||A||U. Legendary||U. Legendary|
|A||A||U. Legendary||R. Legendary|
Each legendary uncommon has a showcase treatment that appears as one of its four copies.
The backgrounds of all rarities are mixed together in one run. This has ten copies of each of the five common backgrounds, four copies of each of the fifteen uncommon backgrounds, and two copies of each of the five rare backgrounds.
The A common run consists of 60 different cards each appearing twice plus one copy of Heap Gate. Other than Heap Gate, the cards appear in a repeating pattern of green, blue, black, white, red. I've chosen to put Heap Gate at the end to emphasize this pattern.
The B common run consists of 15 different cards each appearing eight times. For cards with a showcase treatment, two of the copies are the showcase version. The choice of first card is mostly arbitrary.
The c common run consists of 60 different cards each appearing twice plus one copy of Heap Gate. The choice of first card is mostly arbitrary.
The A uncommon run consists of 60 different non-legendary uncommons each appearing twice. The choice of first card is mostly arbitrary.
The legendary uncommon run consists of 30 different legendary creatures each appearing four times. Each of these cards has a showcase treatment, and one of the four copies is the showcase version. The choice of first card is mostly arbitrary.
 "Commander Legends: Battle for Baldur's Gate Product Overview" by Harless Snyder gives an official rate of 31% to get a legendary creature of planeswalker that is rare or mythic rare in a draft booster.