Urethra diverticulum. Is this serious surgery?

Possibly. Nothing in life or medicine is 100%. Even the simplest procedures have risks. Risks of surgery include bleeding, infection, injury to surrounding tissues, organs, nerves, incontinence, urinary retention, fistula formation, anesthesia reacitions, allergic reactions, urinary urgency, frequency, temporary or pernament pain, disability and death. Balance out the risks and benefits of surgery.
Not usually. 2 ways of correcting urethral diverticulum in female. My preferred method is placing small baloon into d'tic, then excising it via vagina, then repair urthra, interpose tissue & close vagina. Occasional other approach for small d'tics is a transurethral incision to promote drainage. Rarer in males, treated with excision thru incision on underside of penis or urethra. None are serious operations.