Fulltextsearch php fatal error


I have been tasked with setting up fulltextsearch and tesseract OCR on a nextcloud server. When I try to install all the fulltextsearch apps, my nextcloud browser interface becomes a blank page.
In the webserver error log I can read a php fatal error “Declaration of OCA\… must be compatible with OCP\…” for each app.
I am running an apache2 server with a debian10 buster OS.
I am not familiar with this line of work and linux, so if you need further informationit would help me a lot if you provided the command line(s) to acquire it.

Thank you.