I am having the same issue. I used to host a Collabora server, but that stopped working. I tried the Build-in version, but I have the same problem. I’ve removed everything for the time being. Any suggestions would be appreciated.
Most likely your shared hosting cannot meet the minimum system requirements of Nextcloud Collabora CODE.
It actually requires some serious system resources, which are restricted through shared hosting. You must unfortunately install Collabora on a separate server where it can receive the system resources it needs to run properly.
Note these requirements are the absoluteminimum for Collabora for nextcloud. Nextcloud itself requires more!
Linux x86-64 or ARM64 (aarch64) platform
2 CPU cores
1 GB RAM + 100 MB RAM / user
100 kbit/s network bandwidth / user
350 MB space on disk
Nextcloud 19 with Collabora Online app 3.7.0 or higher
glibc (AppImage does not support musl libc)
Fontconfig (libfontconfig.so.1 - required by Collabora_Online.AppImage)