The short answer
Resolution describes image dimensions; codec describes how video is encoded. High resolution does not establish H.265 support, and codec availability must be checked along the whole playback path.
Work through the checks
Use ONVIF-reported media profiles where available, and record the selected profile token. Profiles can differ in resolution, codec, audio and PTZ associations.
Read the codec for the selected camera profile rather than inferring it from resolution or filename. Test a documented baseline stream without changing every encoding option at once.
Compare the main stream and a camera-provided substream at the same time of day. The substream often reduces decoding load, but confirm that the detail you need remains visible.
Lower one camera parameter at a time: frame rate, resolution or bitrate. Re-test motion and readable detail; a lower idle bitrate alone does not prove a usable moving image.
What to verify
Compare the failing source with a known working local source using the same computer. Keep credentials private and use your own authorized devices; do not test unknown public camera feeds.
Sources and scope
AeoCam is available for Windows. Camera settings below describe protocol preparation, not a certification of a particular camera or a promise of every feature in every app version. Check the installed build and the Microsoft Store listing for current availability.
Vendor documents describe the camera or protocol. No physical-camera compatibility test is claimed here. Menus and capabilities can change with model and firmware.