I wouldn't spoil my ballot personally unless I felt every party right now was actively bad. I think there are a few things you should consider:
Some of the parties aren't necessarily the same, policy-wise or values-wise, as they were in the past. They might have the same name as they did ten years ago, but that doesn't mean everything else about them is frozen in time. Parties evolve, and you should judge them as they are now and the direction they're heading in rather than holding vendettas against them for things that aren't representative of how they are now. This is particularly important when parties have new leadership and direction - Labour, in particular, feels like quite a different party to how it was in 2019. Is it better? In some ways yes, in other ways no, I think. But whether you think it's better or not, I think it's distinct enough, and tried to distance itself enough from what it perceived as issues it had in 2019, that holding it accountable still doesn't achieve much. I don't think it's fair to blame Ed Davey's Lib Dems for Nick Clegg's coalition either (although I do think Clegg did a reasonable job of moderating the Tories during that time - things got so much worse once the Tories got full power).
I also think it's important to think of every election as a stepping stone to the future, rather than hoping for perfection to happen overnight. Taking the Labour party as an example, because they're the biggest rivals to the Tories on a national level: do I think things will be perfect if Labour get power? No. They don't necessarily represent my views on some issues, and I actively disagree with them on others. In another voting system, they probably wouldn't be my first choice. But I also think that if Labour gets in, things will move in a better direction. If I think about where I'd like things to be in ten or twenty years, Labour winning this election is probably what ensures the best (or at least most realistic) chance of getting there.
Don't let "perfect" be the enemy of "good". None of the options are perfect as far as I'm concerned. But Labour, Lib Dems, Greens and SNP are all good compared to the Tories, and doing what you can to help the one that gives the best chance of keeping the Tories out in your constituency is going to move things in a good direction. I think that having the chance to actually get rid of the Tories is not the time for apathy, also. I'd hate to see the Tories win again because the left gets complacent or apathetic, or starts splitting the vote because Starmer's Labour isn't perfect. Because do you know what else isn't perfect? Another five fucking years of Tory government. It looks like they're on their way out, but let's not fumble it at the finish line.
Get these right-wing ghouls out of power, and then write to your MP telling them how you'd like to see things change. Because chances are it'll achieve more than spoiling your ballot. Spoiling your ballot expresses that you're angry but it doesn't tell anyone why and it doesn't do anything to bring about change.