SharePoint Online limits

SharePoint Online allows millions of files in a single document library, but does recommend keeping the contents under 50,000 items for search performance reasons.  We find that practically, hundreds of thousands of documents to not have a negative effect on sFiles performance.

When connecting frequently to Microsoft Office 365, according to Microsoft's own documentation, they do not set specific limitations. According to their documentation:

Setting and publishing exact throttling limits sounds straightforward, but in fact it would result in more restrictive limits. We continually monitor resource usage on SharePoint Online. Depending on usage, we fine-tune thresholds so users can consume the maximum number of resources without degrading the reliability and performance of SharePoint Online.

In practice, only configurations where a "Named Principal" is used for auth for a high-volume community will ever even come close to cause Microsoft to throttle down the responses.
To read more specifics on limits, please peruse this document:
Avoid getting throttled or blocked in SharePoint Online

Salesforce limits

sFiles uses flows for setting up the app. Thus, there are some flow limits to consider. If you are running a Salesforce Professional Edition, you will be limited to a maximum of 5 active flows. If your organization already has the maximum number of flows allowed, you may need to either temporarily switch off one of the flows to run the Setup Wizard or configure sFiles manually. Please review this reference:
Salesforce General Flow Limits
 

sFiles Limits

1. Large initial folder structures (greater than 25 total folders) will not automatically set metadata fields in SharePoint. As a result, large initial folder structures are not compatible with community-visible objects.
2. As of Summer 2021, sFiles supports unlimited file size uploads from the sFiles UI, however the sFiles API still has a maximum upload size limit of ~11Mb / file. This is due to the Apex heap size per transaction limit in Salesforce. (https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_gov_limits.htm?search_text=limit)