I’ve seen a spinner before but it would eventually stop after a few seconds. I haven’t seen it at all since eliminating the rich workspace feature that creates and saves readme markdown files in every folder. NC18 allows disabling the workspace using occ in a terminal or with the OCCWeb console app.
See this post:
The workspace will be disabled for all users. You can continue using Text, it just won’t automatically create readme.md files anymore and the workspace will disappear.
If the spinner persists, trouble shooting should start with disabling both the Text and Recommendations apps that occupy that part of the screen. Beyond that you’ll want to examine server settings for Nextcloud, PHP and web server, etc.