Welcome! Nothing wrong with Mint MATE at all. Great way to get a stable desktop without some Canonical-specific (Ubuntu) pitfalls.
I've spent time with Ubuntu, Manjaro, and EndeavourOS with MATE - and I've hit issues with cursor themes occasionally too.
Sounds like a bug or fault with the cursor theme; you could try to adapt this guide to the MATE specific gsettings, the steps will be roughly the same: Customizing Cursors in GNOME | ZoFoss
Otherwise, try another theme (an initial list of packaged themes could be obtained with apt list *cursor*).