Uiua, 39 bytes

⍢(&sl1/4&pf⊂"\rLoading... "⊢.↻1)1$ |/-\

For some reason it looks really slow in the GIF but I can assure you on my computer it waits for 1/4 of a second. You may notice that in the GIF, the code has an extra backslash; that's because I have Uiua 0.9.5 installed on my computer. In 0.10.0, the way $ strings work is a bit different, and the extra backslash isn't needed.

program running

Uiua, 39 bytes

⍢(&sl1/4&pf⊂"\rLoading... "⊢.↻1)1$ |/-\

program running

For some reason it looks really slow in the GIF but I can assure you on my computer it waits for 1/4 of a second. You may also notice that in the GIF, the code has an extra backslash; that's because I have Uiua 0.9.5 installed on my computer. In 0.10.0, the way $ strings work is a bit different, and the extra backslash isn't needed.

Explanation:

⍢(...)1$ |/-\

This starts with "|/-\" on the stack and does the rest of the program in a loop forever. A byte is saved by using the raw string syntax $ |/-\ instead of the normal "|/-\\".

↻1

Rotate this string one character to the left.

&pf⊂"\rLoading... "⊢.

Combine the first character of this with the loading text, and print it. The \r causes the text to be printed over whatever was already there.

&sl1/4

Sleep for a quarter of a second. Using a fraction literal like this is a byte shorter than 0.25.

Uiua, 39 bytes

⍢(&sl1/4&pf⊂"\rLoading... "⊢.↻1)1$ |/-\

GIF coming soon

Uiua, 39 bytes

⍢(&sl1/4&pf⊂"\rLoading... "⊢.↻1)1$ |/-\

For some reason it looks really slow in the GIF but I can assure you on my computer it waits for 1/4 of a second. You may notice that in the GIF, the code has an extra backslash; that's because I have Uiua 0.9.5 installed on my computer. In 0.10.0, the way $ strings work is a bit different, and the extra backslash isn't needed.

program running

Uiua, 43 bytes

⍢(&pf@\b&sl1/4&pf⊂"Loading... "⊢.↻1)1$ |/-\

Doesn’t work in the online interpreter. I’ll add a GIF of it working on my computer later

Uiua, 39 bytes

⍢(&sl1/4&pf⊂"\rLoading... "⊢.↻1)1$ |/-\

GIF coming soon