DIRT 5

As usual all of the events in this series are easy...except the Time Trials, and possibly the Gymkhana event for some players.
I'll comment on a few other event types before jumping into the Time events.

GYMKHANA
There's only one Gymk for the Supersize series.
Do a couple donuts around the loop immediately after you start then head right to do a small jump and drift a few times towards the left to get on the opposite side of the starting walls/high track section to find the purple pad where you can just do 360 Spins until you hit 3 stars.

GATE CRASHER
Take your time on the really narrow sections of track and if you struggle on the loops and sideways sections try the hood or bumper views to make it easier. The 3 star times are generous here so don't fret too much.

SMASH ATTACK
These are easier once you try it a time or two to get the layout of the area. Try to focus mostly on the bigger collectibles which are worth 250 points each and grab some of the smaller ones along the way. Don't worry about collecting every single one as that isn't needed for 3 stars. Never reverse to grab one as that wastes more time than just going on to the next one (unless it's worth 250).

TIME TRIALS
Before you start these, turn OFF Auto-Brake in your settings. It slows you down way too much in the trials.
It's very difficult to win these on the first lap (impossible on most tracks) so consecutive laps will be needed. After you beat the 3 star time you can press Start and select End Event.
The TT's are all about selecting the right vehicle and making tight turns around corners. The AI will always get some weird speed boost on the straight sections of races so you will need to master your agility.

City Bowl - This one is the easiest of the bunch. I used the Porsche Taycan Turbo S to continue working on the 30 miles needed for it's achievement.
Kalabaka Town - I beat this one on my first go around with the Armada Engineering Unlimited Truck but if you feel the need for better handling there are players in the forums who had better luck with the Jackson Adventurer.
East River - Because it's on ice and 30 miles are needed with the Bentley Continental GT Ice Race Car that's what I chose to use and it worked nicely.
Ponti Di Vara - The Taycan or Bentley both work here again but I personally prefer the Porsche. This is one that technically can be won on the first lap if your turning technique is excellent.
Meteora Ruins - I found this race to be the toughest of them all. Your best choices are either the Subaru Impreza S4 Rally or the Mitsubishi Lancer Evolution VI, that latter of which is what worked for me. The S tier handling of the Lancer for tight corners I found to be more important than the S tier performance of the Impreza. Try to stay on the right side of the gate when starting new laps so you can catch a tight first corner to get a lead on the AI right off the bat. Be careful not to catch too much air on the last jump right before the finish line; it will cause you to lose too much speed.
Roosevelt Island - Performance is more important than Handling on this specific trial so the Mini Cooper SXI is far and away the best choice.