Yeah, not the simplest topic and one of the downsides of the flexibility of Xert is that there are loads of ways to use it… and some of the terms can confuse… a fairly common question is what the right athlete type is, including for triathlon e.g. here or here
So time triallist is just a label linked to efforts with a focus of one-hour power = efforts at threshold. So at the most intense (peak phase), your workouts will (broadly) have intervals efforts of around TP (maybe a touch above). That’s by definition not especially polarised (may end up pyramidal at best, otherwise threshold).
Best advice for athlete type is to look at your past TTs and depending on the course (duration, hills, technicality / turns) you may find that you actually need repeated above threshold efforts, which would mean you need a shorter duration athlete type. If you have the power file, look at the focus that is reported for that… and use that choose athlete type… or go one step shorter if you want to do more high intensity
If you have time I’d suggest you do some reading (here, and search the forum) and listening to the podcasts on the topic e.g. episode 3 (but others mention it)… over time it’s also worth listening to all podcasts and reading through the support pages to get an even better understanding