Don't overthink it. There are no standards for job titles in the software industry. Recruiters, HR, and hiring managers already know that title inflation is rampant and "senior" (and titles beyond that) are often handed out like candy. That's why interview loops are long and painful in this industry (I'm not defending it, merely describing the way things are) and tales of "senior" people who are objectively not that good are legion. I usually set my expectations when evaluating a resume based on the number of years of industry experience rather than the job title and that seems to be a common practice.

So relax. If your job title in the HR records was "senior", there's no reason not to put it on your resume.

[EDIT] As a brief follow-up, if the source of your concern is the job titling system used by FAANGs (SWE 1, SWE 2, SWE3, Senior SWE, Principal SWE, ...) as seen on levels.fyi, check to see if your employer is using an alternate job titling system used at a few employers where "senior" is the first level above the introductory level (Engineer, Senior Engineer, Staff Engineer, Senior Staff Engineer, Principal Engineer, ...).