Imports will be the quality of the source, though preview may not display at that quality.
Exports will be whatever you choose. Often it's best to match the source settings.
Please share a file or two that has the issue. Someone will check it out. Upload the file/s to a free server, such as Google Drive or MS OneDrive, get a shared (public) link, copy the link and paste it here or to me in a Private Message via the mail envelope in the top-right corner of this forum. When using Google Drive, if necessary change "restricted" to "anyone with link can view."