As above really: Which workout on the trainer would you recommend for honing your bike fit? Handlebar rotation, saddle angle, saddle height, saddle fore/aft, stem angle. bar height, cleat position etc etc etc
You would be jumping on and off the bike quite a bit to make tweaks.
Obviously you won’t ever get real-life road vibrations and only long rides of the style of riding you do will confirm your fit is good.
I use the lighter rides Petit/Baxter etc… next day I make sure through the warm up of the harder workout and if all feels good I push on - if not I tweak a little and carry on.
I find trainer rides and in particular the light endurance ones ideal for this kind of tuning.
For fitting purposes, the basic guideline is to do a workout or effort that is around what you expect to be doing for the majority of your efforts on the bike. That may mean relatively easy for a touring rider, vs near Threshold for racers.
It really depends on you and how you plan to use the bike. Think about your most common efforts and try to mimic that within reason. There is no one right answer for everyone.
Honest answer is that jumping on and off the bike multiple times per ride and adjusting all the things you list sounds like a terrible way to hone your bike fit! There’s going to be so many moving parts it will be almost impossible to isolate what’s working and what’s not, plus if you’re doing that much fiddling then you’re not giving your body a chance to adapt to any of the changes. You might hit on a good bike fit but I would say if you do it’s more likely through good luck than good judgement.
If you have existing bikes set up in a way that works for you, then you should be able to set up a new bike close enough that you’re only having to make one or two minor changes at a time just to fine tune things a little. Ideally one at a time, but some changes impact others e.g. moving your saddle forward will also slightly reduce the nose to bottom bracket distance so in order to keep saddle height consistent you should raise it slightly.
If you’re new to riding and don’t yet have an established position that you’re happy with, then I would go see a fitter.
If you’re set on taking this approach I wouldn’t even try and combine it with any particular workout, would just free ride so that after each change you can try a number of different intensities and durations to get feedback. E.g. I find it more comfortable to hold an aggressive position (sitting right on the nose of the saddle) when I’m pushing higher watts which is effectively taking more of the weight off my butt.