Turn your InstantPot on "Sauté" and select "MORE" mode. Add in oil and allow to heat at least 3-4 minutes.
Season beef with salt. Add to InstantPot and brown the meat by stirring every 2 minutes or so. Should take 5-7 minutes to brown on all sides.
Add in onion, carrot, celery, and thyme. Stir to incorporate with beef, and continue to sauté all ingredients for 5 minutes, stirring occasionally.
Press "cancel" on the InstantPot. Add in beef stock and potatoes (if using), along with any vegetables that will not turn to absolute mush in pressure cooking (parsnips, some squashes/zucchini). If you aren't sure, I suggest blanching or simmering the "weaker" and "mush prone" veg at this step SEPARATELY from the InstantPot.
Ensure lid on InstantPot is closed properly and set vent to "seal". Press the "Soup" function button, or alternatively choose Pressure Cook at "Normal" for 30 minutes.
Once InstantPot completes pressure cooking, rapid vent the pressure and open the pot. Add Worcestershire Sauce and any frozen or fresh veg that didn't need to pressure cook, including any you blanched or simmered and drained. Stir gently (as to not break up potato if you pressure cooked it) to combine. Season to taste. Simmer/heat until vegetables are cooked the way you want them.