Solo Tactics
You've seen how teams can split objective responsibility. When you're solo, everything is your job. You'll need a loadout that can cover Thrax killing and trash killing equally as effectively.
Playstyle
When solo in Void Cascade, you're limited to four Exolizers active at any one time. The smoothest gameplay loop is a playstyle that reflects a Dedicated Defender in a team. You purge all Exolizers in the current room, then you stay to defend them. Even when more Exolizers begin to spawn in the next room, you stay to defend. The scales begin to tip out of your favour - as you're defending the last Exolizer, three possessed Exolizers are very likely already waiting for you in the next room. This is where you brute force the meter down by killing enemies within the golden Exolizer circle. Once the diamond of the last Exolizer is down to ⅛, you move on.
As you enter the next room with three or four possessed Exolizers waiting for you, depending on the state of the meter, it's sometimes best practice to prioritise purging the Exolizers and ignoring Thrax until you're done. Then you take on three, four, or more Thrax at once. Don't worry, you've got this.
Rotations
The main thing to watch out for when playing solo is that the Exolizer rotation can be all over the place, and not follow such a strict and neat order as when in a team. What your rotation decides to do varies a lot depending on the rooms you get.
For example: your rooms are Garden (A - 3 spawns), Serenity (B - 4 spawns), Theatre (C - 3 spawns). This should mean your rotation is: 1A -> 2A -> 3A -> 1B -> 2B -> 3B -> 4B -> 1C -> 2C -> 3C -> Refresh to Room A But what do you actually get? 1A -> 2A - > 3A -> 1B -> 1A -> 2A -> 2B -> 3B -> 1C -> 2C -> 3C -> Refresh to Room A (Real life example taken from one of my solo runs)
Sometimes a weird rotation order sorts itself out after the first 16 Exolizers. Sometimes it doesn't, and it's up to you to manipulate the order of the Exolizer spawns into something more convenient.
Manipulating Rotations
Sometimes a weird rotation order sorts itself out after the first 16 Exolizers. Sometimes it doesn't, and it's up to you to manipulate the order of the Exolizer spawns into something more convenient.
For example: your rooms are Park (A - 4 spawns), Hall (B - 3 spawns), Hangar (C - 5 spawns). Your rotation is doing this: 1A -> 2A -> 1B -> 3A -> 4A -> 2B -> 3B -> 1A -> 1C -> 2C -> 3C -> 4C -> 5C -> Refresh to Room A Ignore Exolizer 1B and purge and defend 3A and 4A. The rotation will then take you to Room B where you can continue as normal. Then, ignore 1A and deal with Room C. The refresh will then take you back to that rogue 1A. The rotation will hopefully follow the order the previous Exolizers completed, as dictated by you, and the rogue 1B and 1A shouldn't happen again.
Manipulating the Exolizer rotation is something that comes with practice and experience - you'll know when it's safe to ignore an Exolizer or when it would be too risky to do so. Thanks to the limit of four Exolizers active at a time, solo level cap runs are perfectly possible. My main piece of advice is to be quick and efficient with your parkouring from Room C back to Room A - you're tight for time.
Enemy Aggro
Something to keep in mind is the intensity of enemy aggro while playing solo. While you're in Operator, your parked Warframe will be drawing aggro if it's not stealthed. If you have a channelled ability or some duration abilities active, this means it will be vulnerable to 10% of incoming damage (hyperlink). If it "dies", you will be yanked out of Operator back to it with 2hp and no shields. Alternatively, if your parked Warframe is stealthed, all aggro in the room will be on your Operator when they're out of Void Mode. Both of these scenarios encourage you to deal with the Operator sections of void tears and Spectral Thrax as quickly as possible - there is much more pressure on you when solo than in a team.
There is some footage in the footage page(hyperlink) showing solo runs, where you can see how to handle Exolizer rotations.