Max : Have you tested for spark yet by grounding the plug against the head or utilized a spark tester ? You should visualize a bright blue spark from a sound coil and new plug.
Otherwise have a service professional do a load test on your coil unit . You can easily test your on off switch with a multi meter accurate testing of your coil requires an experienced tech . let us know the outcome ...E !

Don't rule out a fuel problem yet. Do have the special screwdriver needed for adjusting the mixtures? To check for fuel starvation, Take off the plastic cover, flip the choke lever to 'Run' and pour about a teaspoon of 2-cycle mixed fuel into the air intake. Set the choke lever back to 'choke' and see if it fires up. The mixture screws tend to turn lean. I don't know how they do this since normally if they moved you would expect them to turn 'out' resulting in a rich condition. This trimmer likes a very rich condition for starting; up to ten primer pushes and choke 'on'.

What is the special screwdriver?

Yeah, that's what the owner's manual says, 10 or 11 primer pumpings

I will. Want to go back to committing more vegicide.

Do you know where the needle valves are? Once you find them see what method is used for turning them since they don't have any accommodations for regular tools. They should each have one notch on the edge of the head. The tool is a hollow-shaft driver with a rib inside that fits the notch. You can get one on ebay for $2.00 but Ryobi won't sell you one. Once you give it some gas, you'll find it starts easy and revs up to where it should.

I use a Dremel to cut the screwdriver notch, There is a oval guard which i cut into also.
Too many types of drivers needed.

I noticed you said " checked the fuel line, it was passing gas"
That does not mean fuel is getting into the fuel bowel.
I see 90% of most weed eaters have a clogged screen.
Ethanol does this.
When the fuel lines get older they break or let the fuel line filter fall off and you get garbage into the carburetor.
Every weed eater fixed gets new fuel lines and a filter.
All carburetors are cleaned and inspected.
And 90% have clogged filters.
Once again jet tools are a pain in the butt. Too easy to loose.
And the jets are adjusted only when the unit is up to temperature.

Welp, this was a "new" weedeater, in that it was reconditioned to like new condition, with parts such as the primer bulb(the little rubber button that you press many times in order to help the engine get started. I've noticed in other weedeaters that are a few years or older the primer bulb does degrade, which is not only crackes, but also it is more stiff than usual),the fuel line, and other parts, including the spark plug. Where is the screen? Is it on the end of the fuel line, the part of the line that goes into the carb bowl(if it has a discrete carb, and not a needle jet in a venturi, as some small two cycle engines have, such as model airplane engines)? What else would degrade? This was working really good one day, then the next is wouldn't start, no matter how much priming I did, or pull on the starter(pulling the starter is too much work, if it doesn't start fast, which my Ryobi did, and there are easier ways to get exercize)

I cant remember which it was the Mantis or the Husqavrna 322L , On one of them, the fuel line going to the pickup/ filter broke off inside the tank. . The line had turned to mush as well. One minute it ran, next it didn't.

If it is new then take it back. How new is new??