Understanding Excel 365 Connector Limits

Import

Defoult mode
in the “default download” mode, due to available API, the maximum number of downloaded issues is 3000. Depending on the filter used or JQL structure, the first 3000 issues will be downloaded.
Read only
in this mode, the maximum number of downloaded issue is 100,000. In this mode, it is not possible to edit issues, its a raw data.

Export

Export issues from Excel to Jira allows you to send 500 issues at a time, regardless of the type of license you have. If there are more Issues, press the Export button again after sending the first batch of issues.

Restrictions on data editing

Certain data is uneditable due to various reasons such as insufficient permissions or API restrictions, and are therefore displayed in gray cells. These data are designated as 'read-only'. Attempting to edit them will trigger a visual indication in red along with a corresponding message to notify users."

Here you will find more information about cell Colors

JQL

It's the query language used in Atlassian's issue tracking and project management software, Jira.

it may not support highly intricate queries or advanced data manipulations that some users might require;
queries may not work with custom fields if they are not properly indexed in Jira;
Users may only be able to query issues for which they have appropriate permissions;
Some JQL functions or capabilities may rely on specific plugins or add-ons installed in Jira.