Here's a few examples of how things should have been done.
Wall to shingles details.
Roof vent install.
Notice there's no exposed nails on the lower side and the shingles cover all the metal on the sides and top of the flashing.
The OSB never should have been used as soffit material!
If that was mine I would reframe that low slope roof so it was steeper.
Get rid of those ugly turbine vents and install a ridge vent instead.
Remove any of the old rotted 1 X's and replace with PVC or wrap the metal wood with coil stock.
Plus about a dozen other items that were done wrong.
The first warning sign I would have seen if I was buying this house would have been all the roofing tar all over everything.
Done right there would have been no tar needed.
Your talking some pretty involved work here.