The Core

>will not recommend any pressure washer with a 0-degree tip.

Likely because of the potential for damage and injury. See above.  Doc's 3200# with a 0 tip can chip a concrete driveway *IF* you get it too close.  Dropping to a 15 with double the time for the same job.  I also use a pw like a leaf blower and the 'punch' from a 0 is waaaaay better.  I have a whole jar of 15s-40s that I'll give you, hhh.

>dig a hole

Be prepared for a helluva muddy blowback,  but -yeah- it'll dig.  You & Doc might consider a drill-driven garden auger to help getting the bore under sidewalks and roots.
https://www.amazon.com/gp/product/B000LNTO8A

>where the hoses are interchangeable and the connectors are standard?

99% yes. I have run into one wand from SunJoe that tried to be proprietary.  Connectors for the tips are 1/4" and the hoses are 3/8". For example;

These 3 items connect to the end of the wand, so they are 1/4"
https://www.amazon.com/gp/product/B07TSCX5T6
https://www.amazon.com/gp/product/B07T3JNLTQ
https://www.amazon.com/gp/product/B07T4JY32M

The hoses and the inlet on the gun handle are 3/8", like so
https://www.amazon.com/gp/product/B00GN51RB2

>on the sides

Yeah, you're going to need a trench on the starting side that's at least as long as the width of the sidewalk.

They make a sewer jet for pressure washers that split the water direction. One points forward to clear or bore and the rest are directed to the rear to provide propulsion.

https://www.amazon.com/gp/product/B07RPY26GZ

I've used these a few times on commercial properties as well as my home. Work very well.  The surprising part is they develop enough power to drag the hose along, too.  Since you have rental property you might want to add one to your bag o' tricks. Cheap.

For a horizontal bore under a sidewalk, I'd start with the auger, maybe adding an extension to bore as much as possible with the drill.  Then I'd drive a 1" or 1-1/4" piece of pipe the length of the it roughly the width of the sidewalk in the bore hole.  I'd put the sewer nozzle through that pipe sleeve to finish the bore, tapping the end of the pipe with a mallet as the jetter worked.  The idea is that the jetter will flush out the dirt through the pipe. 

>>  sewer jet

You are a font of wisdom. Never heard of such a thing. Never would have thought to look for such a thing. It seems like a useful tool for "soft" clogs. I.e. not tree roots growing through sewer pipes, which is a common problem here, but useful for sh## and TP in the pipe and maybe other things that shouldn't get flushed but do, like the billions of dollars of damage done around the country by "flushable" wipes.

+

Commercial cutter blade (scroll)

https://spartantool.com/informationcenter/resources/sewer-jetter-applications

Purchased - Greeworks Pro

https://photos.app.goo.gl/5MVD7mcoorMtk3xe9

Results
https://photos.google.com/photo/AF1QipPq1Qskli5djjo0ffkOsI8C9eMEoWn-KaFLvz45

Doesn't look that impressive, but the dirty part had previously been scrubbed with soap and a brush.