The angle of the rear handles are horrible for hanging a suit jacket in my 2021 ES.

Are the any good products that solve this problem?

 

Wrinkle proof suit jackets!😜

 

You do know there's coat hooks provided with the rear assist grips/handles?

See page 289 of the 2021 Lexus ES250/ES350 Owner's Manual. When using the coat hooks you should heed the manual's warning:
Quite a few, if not all, suit jackets (as well as many other types of coat) have a hanging loop sewn into them on the inside near the bottom of the back part of the collar. Use the suit jacket's hanging loop and the coat hooks to hang your suit jacket.

Unless your suit jacket's material is chain mail or metal plate armor, using the jacket's hanging loop also heeds the hard or sharp object warning.

 

I always wondered what would happen if you're holding onto the grab handles (driver or passengers) when the Side Curtain Airbags deploy?

This also reminds me to be aware of your arms on the armrest and the steering wheel too. Lots of people end up with broken hands/arms because they were positioning them weird when the airbags popped. basically for safest results, drive like a crash test dummy at all times!