(Male) What are the chances of contracting a UTI from unprotected anal sex?

pitching or catching?

Pitching.

Yes. Wear a condom.

UTI needs antibiotics else your pecker will fall off then no fun.

Between the anal ring and the rectum is a pool of bacteria, not friendly bacteria. It is also the case that if either party has STD's or any other issue such as Hepatitis, then that is more easily transmitted in the anal/rectum region than other areas except for the eye socket which is #1 transfer port into the human body.

Even if you are in a 100% monogamous relationship then you must wear a condom. It doesn't matter if the recipient has had an enema, douched as well ... it is still a haven of negative bacteria.

If the condom breaks then urinate as soon as possible, within seconds .... Warm, fresh urine is sterile and will help to flush out anything which has entered your urethra ... That is an emergency measure however, not a 'fix' to not wear a condom.

Always wear a condom, entry hole immaterial is my advice. If you don't realise, I have a great deal of M/f anal experience and have never caught anything from any partner in 40+ active years.

Fair chances.
Have had UTI twice once from valinal sex (I am male). Once form anal. Have been active for 40 yrs. Really good sex is a contact sport. But I have always been very selective about with who. These are my choices, no whining.