There's no way to automate sentence case, I'm afraid, see https://www.zotero.org/support/kb/sentence_casing for details.

No, see the linked page — the point is that there's no way for any tool to automate conversion to sentence case. It can't be done reliably by a computer, because a computer can't reliably recognize proper nouns. This isn't going to work better in another program.

As explained on the linked page, you can right-click on a title in the right-hand pane in Zotero to do a naive conversion to sentence case, after which you can correct any proper nouns.

Zotero has exceptionally good support for APA, and a huge proportion of Zotero users use APA. This is just something you'd have to do in any tool.

About 35 years ago an experimental (DOS) version of Reference Manager had a sentence-case conversion utility with a look-up table (similar to the user-modifiable spelling dictionary) that allowed proper nouns to be added. The shipped-with table included all manner of place names and biological names. It was slow. While the table contained major place names most names needed to be added by hand in a tedious several-step process. [Pre-mouse: tab and key-combination to fill forms era]

The standard version also allowed entry of several (I think up to 3) different journal name abbreviations. One of the abbreviations was to facilitate hand-entry of journal names. I remember using '=aap' for "Accident analysis and prevention" and '=jsr' for "Journal of safety research".

edit: Shortcuts for hand entry were essential because, if I remember correctly, import formats were limited to Medline-tagged format and RIS. There was a cottage industry of people who created RIS files from current contents of selected journals. The files were distributed by (snail) mail on 5.25 in floppies. Obtaining a Medline-tagged file was complicated and costly. This was more than 10 years before PubMed. Medline searches were performed by special librarians via a smart teleprinter only some of which allowed files to be saved to floppy disks. Medline searches were quite expensive with tape-change charges when searching multiple years.

The RM experiment didn't get incorporated into a production version. Nonetheless, I continued to use the experimental version (with shortcomings like @adamsmith mentioned) until a new RM version was released with some desirable enhancement I valued more than the title utility. Perhaps a better example would be 'The makers mark their completed work with an identity stamp and celebrate with a glass of Makers Mark."

edit: If I recall correctly the enhancement was the use of a proprietary system that allowed recognition and storage of characters with diacritics where before the only allowed characters were basic ASCII.

If it's a design decision that's been made final, just say so :)