Use the table of contents to navigate to whichever mission you're currently doing. The numbering order was determined on a whim and is not indicative of a suggested path.

Yellow box -> chest or loot
-This icon covers all types of chests as well as the 'unidentified blueprint'. The icon's size is not indicative of what type of chest/loot is there.

Blue 'Diamond' -> info-fragment
-For revealing the contents of end-crusade loot chests. Omicron Arkh has a voice line that lets you know when one is nearby. (I realize this icon is pixellated in the mission maps)

Red Box -> cogitator for unlocking secret missions
-When the cogitator is activated, Omicron Arkh uses a recycled voice line from the previous two void crusades in which he mentions a covert mission, but there are no covert missions in this void crusade.

Purple Oval -> teleporter
-Only teleporters that go to "off-map" rooms are marked.

Green Star -> relevant secondary objective
-Only secondary objectives that unlock something upon successful completion are marked.

Note about the crusade map:
The small yellow number in each mission icon is the corresponding difficulty increase.

Note about the mission maps:
I've rotated them to at least approximately match how the map is oriented at the start of the mission.

https://steamproxy-script.pipiskins.com/sharedfiles/filedetails/?id=2192043784
The numbers have been converted to my numbering.

"Path through the Void Crusade"
1 - 2 - 5 - 7 - 12 -
11 - 13 - 14 - 9 - 21 -
17 - 18 - 4 - 6 - 19 -
20 - 22 - 10 - 16 - 8 -
15 - 3 - X

"Path for the +10 difficulty mission seasonal challenge"
1 - 3 - 8 - 9 - 16 -
17 - 14 - 15 - 4 - 6 -
7 - 5 - 22 - 18 - 19 -
21 - Z

Completing this mission unlocks Secret Mission 6.

Unlocked via completion of mission 4.

Using the cogitator in this mission or the cogitator in mission 12 unlocks Secret Mission 11.

This mission is unlocked via the cogitator in mission 9 or the cogitator in mission 12.
Must successfully aid the Stormwatcher to unlock the cogitator which unlocks Secret Mission 13.

Using the cogitator in this mission or the cogitator in mission 9 unlocks Secret Mission 11.

Unlocked via the cogitator in mission 11.

The cogitator in this mission unlocks Secret Mission 19.

Unlocked via the cogitator in mission 18.

Nothing here.

Let me know if I missed anything or if there are any typos/formatting issues.

Credits:
https://steamproxy-script.pipiskins.com/profiles/76561198092241169 for the 6/7/23 update

Patch notes:
4/01/20 ->
-fixed the crusade map
5/025/20 ->
-linked the amber guide
6/26/20 ->
-linked the viridian and azure guides
-noted which links go to which guides for ease of reference
10/13/20 ->
-updated the Crusade Map with the difficulty increases
-added a new note in the map key
-added notes under certain missions and updated the titles of certain missions to make unlock conditions easier to reference
-linked the Zircon guide
2/12/21 ->
-linked the Violet guide, linked a fellow guide-writer's void crusade path recommendations
8/4/21 ->
-linked the Crimson guide, updated the map for mission 12 (one of the chests was removed)
6/7/23 ->
-added a section for Grimstalker's recommended paths
-changed the link to Grimstalker's stuff from the general link to the link for the specific crusade and moved it to the dedicated section from the basic guide info section