Amazon has some odds and ends for cutting rounded corners, even for cutting the camera slot in a cell phone case. Some of these are pretty light weight, corner punches etc. aren't as nicely finished as the pictures show, but would do for occasional use. For heavier duty, go to the Longview Leather, SLC, Weaver, etc.
Some examples that you might be interested in from Amazon;
https://www.amazon.ca/Trimmers-Leather-Trimmer-Leathercraft-Cutting/dp/B07YZFMFF4/ref=sr_1_296?crid=SJADCY46YC87&keywords=leather+tools&qid=1672700992&sprefix=leather+tools%2Caps%2C128&sr=8-296
https://www.amazon.ca/Leather-Punch-Cutter-Tools-Hollow/dp/B08R694896/ref=sr_1_241?crid=SJADCY46YC87&keywords=leather+tools&qid=1672700952&sprefix=leather+tools%2Caps%2C128&sr=8-241
https://www.amazon.ca/Leather-Craft-Hollow-Cutter-Plastic/dp/B07NZPFR16/ref=sr_1_200?crid=SJADCY46YC87&keywords=leather+tools&qid=1672700886&sprefix=leather+tools%2Caps%2C128&sr=8-200
https://www.amazon.ca/Baitaihem-Leather-Half-Round-Cutter-5mm-50mm/dp/B09YCQWNWD/ref=sr_1_153?crid=SJADCY46YC87&keywords=leather+tools&qid=1672700829&sprefix=leather+tools%2Caps%2C128&sr=8-153
https://www.amazon.ca/DIUDUS-V-Shaped-Leather-Cutting-Cutter/dp/B09YNT6SKW/ref=sr_1_55?crid=SJADCY46YC87&keywords=leather+tools&qid=1672700718&sprefix=leather+tools%2Caps%2C128&sr=8-55
https://www.amazon.ca/Hollow-Cutter-Leather-Cutting-Handmade/dp/B09XDGF7GX/ref=sr_1_56?crid=SJADCY46YC87&keywords=leather+tools&qid=1672700718&sprefix=leather+tools%2Caps%2C128&sr=8-56