I’m absolutely no expert at weight training and have not yet seen a generally accepted way to judge training stress for them.
I do my (limited) strength training as body weight training and use HR TSS. But doing burpees (that’s what I mostly do) is both strength and cardio and very different to weight training.
If Suunto let’s you enter RPE and that makes it to Intervals, you could try that to see if it fits your needs.
There’s also “Weight Lifted”. But I don’t think anything is implemented yet. Here is a thread with similar question.