The zoom effect is being effected by the "FOV Effects" slider inside Video settings, which it did not do in previous versions.

Steps to reproduce:

1. Adjust the "Video Settings > FOV Effects" slider to 100% and try zoom in with the spyglass
2. Adjust "Video Settings > FOV Effects" slider to anything lower than 100%
3. Zoom in using the spyglass.

Observed results:
Zoom is directly affected by the FOV Effects slider, such that setting it to 0% causes the spyglass to not zoom in at all.

Expected results:
Spyglass zoom should be unaffected by the FOV Effects slider (as in previous versions).

Everything I have tested has been in vanilla versions of the game, no mods used.

The specific example here that I am using to compare zooms is just me creating a 4 block wide gap and zooming in from one side to the other to directly compare how the block appears. I have attached how setting FOV Effects to 0 appears in 1.21.1 and how it appears in 24w33a. One of my versions is set to windowed, as screenshotting with windows doesn't work properly in 1.21.1, but swapping to full-screen does not change the results.

1.21.1:

24w33a: