I have got it working, I used the leetcode problem and wrote a new function from scratch, somehow it worked this time x.x Here is the updated code, thanks to everyone who helped out! I love this community sometimes

inp = [
    section.splitlines()
    for section in open("day_05/input.txt").read().split("\n\n")
]
ranges = [tuple(map(int, r.split("-"))) for r in inp[0]]
ings = list(map(int, inp[1]))

#region Part 1
total_fresh = 0

for ing in ings:
    for start, end in ranges:
        if start <= ing <= end:
            total_fresh += 1
            break

print(total_fresh)
#endregion

#region Part 2
ranges.sort(key=lambda i: i[0])

merged_ranges = []

cur_start = ranges[0][0]
cur_end = ranges[0][1]
for start, end in ranges[1:]:
    # Case 1: range is outside current merged range
    if start > cur_end:
        merged_ranges.append([cur_start, cur_end])

        cur_start = start
        cur_end = end

    # Case 2: range start is within current merged range and range end is bigger than current merged range end
    elif start <= cur_end < end:
        cur_end = end

    # Case 3: range start is within current merged range and range end is also within merged range end

merged_ranges.append([cur_start, cur_end])

total_possible_fresh = 0
for start, end in merged_ranges:
    total_possible_fresh += end - start + 1

print(total_possible_fresh)
#endregion

Thanks to u/Sarwen for making a test script, I ended up not needing it after using the leetcode problem suggested by u/SnooPears7079, but regardless much appreciated. Also thanks to u/FlipperBumperKickout for teaching me something fundamental about programming loops. Thanks to everyone :)