Can I increase rendering speed by linking two computers?

I have two computers, connected via my LAN, running Nuendo. Is there a way to use the CPU in the second computer through the LAN to increase the rending time by somehow syncing them up?

Yes, it should work with cluster computing with MPI. Windows and OSX.
To do this, you should look for a specialist. This has nothing to do with Nuendo - but with how you bundle computing power. It should work - but you need an expert to implement it.

Well what is it you do for work? Is this a music session with a heavy VST instrument followed by a super-long chain of heavy plugins where all heavy work is done in series, or is this a moderately “long” post project with a ton of tracks with processing being more parallel?

If your processing speed is limited by a single long chain of processing then I really doubt it would be faster with a second computer. If it’s all parallel processing then maybe yes.

My hunch says that whatever you do to speed things up it’ll likely be cheaper and less hassle to upgrade the computer.

As a small in-house Production house we had 2 Davinci Resolve workstation running on Linux each with 4 Nvidia M6000’s and a render that would take 18hours on a normal gaming PC would get done in 30 min. This includes Dolby Vision and Dolby Atmos.
The workstation was primarily intended for Fusion and Blender/Octane but worked fine for Resolve. The setup and networking were all on fiber.
Long time back our FCP used to run of Promise/Xsan servers.
After our studio closed down in covid and we moved home we sold one.
We still use it for Blender animation as you can see HERE

Today you get the same performance with a Mac Ultra and a fraction of that cost and we are mostly using the one single Lunix workstation that we didn’t sell for Fusion/Unreal/Blender renders.
The M1’s are smaller than a shoebox and I can run it in my Bedroom studio, don’t need AC and don’t need to run on an Industrial meter.
So you need to weight the pro and cons against cost benefits.