Help diagnosing Blown trans

Last night my 2007 Scion TC broke down, what happened was i was going
80mph or so down the freeway, then slowly but surely 5th gear started
feeling like neutral, then 4th, then all of my gears became neutral. I also lost
complete and total pressure in my clutch and it was even stuck to the
floorboard momentairly? Fast forward to an hour ago, and i was able to start
my car because my clutch had all of its pressure back again? And when i
started the car i was able to put it into first gear and move it about 30 feet
forward in my driveway before it eventually turned back to feeling like neutral.
Few days prior and leading up to the event i smelled a bad burning smell but
i assumed that was my "incorrectly installed valve head cover gasket" leaking
oil and i was smelling a burning smell from that, looking back on it that "burnt
popcorn" smell was obviously my clutch and my clutch was obviously slipping
for days before this happened.

Some extra information, I'm pretty sure my transmission fluid is 40,000+
miles overdue for a change. extra info but when i turn my car on, i need to
hold the clutch to shift into any gear and the gears feel somewhat fine, i don't
feel like there's a problem with the gears. and of course when the car is off it
can shift into any gear. Also turned the car on, held the clutch for 15 seconds
then tried to shift into a gear & it worked perfectly fine.

I'm looking to fix this problem myself and i have no where else to turn to for
help in diagnosing the issue, I'll provide any and all
videos/pictures/information to whoever can help ):

update: slave & master cylinder show no signs of leaks. however my brake
fluid reservoir (clutch & brake fluid share the same reservoir) is at the
"minimum" level, so i plan on filling it up tmr and checking for a leak.

Information -
2007 Toyota Scion TC
187000 miles
2AZ-FE 2.4l Engine
5 Speed manual transmission