My PhD seems daunting and overbearing. How shall I regain motivation and interest?

my supervisor (...) keeps saying she has no concerns

Believe her.

Having lots of comments and suggestions for improvement does not mean she doesn't like what you have done. It may be the exact opposite: because she likes what you have done, she wants to make sure your research is presented in the best possible way, clearly demonstrating its potential and value.

I would suggest taking some time off to recharge your batteries and then working through the list. You've made it this far, now do what it takes to complete your PhD. Judging the value of the research is most likely better done in a less stressful situation (i.e. once your done).

First, I think that your first paragraph is a bit at odds with the rest. If I read it correctly, you are in a good place even if your current "mood" is down rather than up. But that is a common reaction for a grad student, especially one who is aware of things. One reason for thinking your research isn't very valuable is that you are now, unlike a year ago, understanding it much better. Before it seemed hard. Now it seems routine. But that is an effect of your mastery of it.

I suggest that you think both short term and long term. In the short term you want to complete your degree and move on. Changing your path radically now might negatively affect that. You have made some progress.

But thinking long term, you may also want to move to a somewhat different subfield. There is no reason you can't do that, but it would be easier to do so after you finish your degree and have a regular position. But you don't have to completely abandon thinking about, and taking notes on, the new field while you pursue the main thread toward completion.

I've recommended in a number of other posts here that researchers keep a research notebook in which they record ideas for research that might be explored and developed in the future. When any idea of potential research directions occurs to you, make a page in the notebook for it. Periodically review the notebook and update it whenever related ideas occur. With judicious use you can keep fairly current in a somewhat different subfield without abandoning the path you are on.

The advice you are getting seems to be good. Don't let it confuse you, however. Deal with the short term to enable the long term. Your first work (dissertation) isn't likely to be your best work over a long career.

One of my PhD professors told us something like this: "Make sure that you pick a topic that you absolutely love, because by the time you're done, you're going to hate it." I've found this to be an excellent piece of advise. The PhD journey is so intense and soul-consuming that you should not go that road on something that you're not emotionally invested in. By the end of the road, students are often sick and tired of their deep dive into the same topic over a few years, so it's best to start with something that you really like to begin with.

You don't have to literally absolutely love it (in fact, there are problems with taking that too literally), but emotionally, you do need to like your topic a lot and you certainly need to believe in its importance. Put aside your need to convince your committee: you need to first focus on convincing yourself. So, rather than trying to motivate yourself in your topic, I strongly suggest that you switch topic for something that genuinely motivates you.

That said, resource support is very important, and this comes primarily from the professors whom you are working with. So, I generally recommend to PhD students to look for a topic or sub-topic that a cooperative professor is already interested in, and then go with that for the PhD. If you can find a topic that you like that your potential supervisor also likes, then they are emotionally invested in supporting you and you will find that your PhD journey goes much more smoothly.

So, in brief, I recommend that you carefully examine the topics and sub-topics of interest of the supportive professors that you have access to, then pick the one you like best as your PhD topic.