Getting an error like on SPFX webpart "Deploying a domain isolated package on a site collection app catalog is not supported."
It seems like in your web-part the
isDomainIsolated property to
true in the
Change the value of this property to
false and then package your web-part and re-upload it in the app catalog.
Check more about Isolated web-parts in below link.
Reference: Isolated web parts.
When you scaffold a new SharePoint Framework project, the SharePoint Framework Yeoman generator will prompt you, if the solution requires API permissions that should be isolated and not available to other components.
If you answer Yes, then the generator will add a flag to your project's configuration in the config/package-solution.json file, by setting the isDomainIsolated property to true.
Looks like you have set
"isDomainIsolated": true, in the
Modify it to
"isDomainIsolated": false, and then do the process to package the solution again by doing the gulp tasks and then re-upload the app to the site collection app catalog.
Usually, domain isolated webparts are used for communicating securely with resources outside of SharePoint and rendered inside iframe. Also, these can sometimes request permissions which require tenant admin's permissions, so they can't be installed in site collection app catalog.