ciao hm11, i hope your are having a stunning weekend wherever you are and doing whatever you do.
my impression (take it or leave it) is that you may have wrongly indentified what you feel to be you 'problem'.
so the struggle and tension you feel (and that you consider to be your 'problem') when you sit down and try to work in a linear way to complete a song (as you explain you are trying to do), may simply be because you are someone who instinctively works best (in accordance with your nature as a creator) in a non-linear way.
working in a non-linear way being breaking down a big and overwhelming linear project into seprate smaller projects, that can be worked on in a non-linear way. each existing in various stages of completion, all open and available to you at any one time.
from which collection or 'pool' of parts and ideas, you can eventually draw from one resolved song, by mixing and matching according to mood and taste.
therefore the current bog you feel you are stuck in and making no progress with, may ultimately be a symptom of self-inflicted 'organisational issues' as a consequence of trying to work in a linear way when you are a non-linear creator.
in which case, you may want to think differently about (or at least experiment with) how you organise your workflow, by separating things out a bit more, and trying to work in a less linear way for a while?
as a first step, perhaps try separating out what you may consider the 'verse' part from the 'chorus' part (if your song can be divided in that way).
work on the verse as a thing on its own (away from the chorus) with a spirit of its own and a mood and dynamic of its own.
and work separately on the chorus similarly. so you have two threads or streams (each containing a separate idea) to skip between and work on simultaneously, rather than have all your eggs and all your frustrations in one basket you feel duty bound to slog away at, with ever decreasing returns (because stress is the mortal enemy of creativity).
let them expand or shrink, and grow in all directions (add things infront of them or after them), if that is where they seem to you to want to go.
maybe you will eventually decide to rejoin them as chorus and verse once you have worked through and resolved each as separates.
or maybe they will become two things, one of which you can finish now, and one which will remain unfinished until a late date.
and when you feel yourself getting frustrated with one. take a break and try working on the other.
working on two things simultaneously that you can move between as and when you get stuckwith the other, will reduce your stress levels and jump you out of your linear groove into a no-linear way of working that you may find is more suited to your nature.
finally give this 'in discussion' with brain eno some consideration (whether you care for his music or not).
the way he explains the way he works as a film score composer follows a similar idea to what i describe above (keeping many unresolved pots of ideas on the stove at once). maybe his explanation of what he does and why will resonate with you better than i have tried to describe here
another important thing he touches upon here is that of creators who work exclusively in the digital sphere suffering from something i call 'option paralysis' or 'option overload'. this may also be a part of your 'problem'. again not really a 'problem' in you, but a problem inherent in the tools you use.
Brian Eno on Exploring Creativity https://youtube.com/watch?v=JUL8kNYmgsA (use the invidious or piped front end to avoid google)
good luck and i hope you can find a way of resolving your struggle one way or another.
Olivia