That’s not a correct Discourse URL, that would be
New url style: https://forum.xxx.nl/t/---topicname---/TOPICID?page=33 (Discourse style)
And you would need a mapping from bbPress topic slug / page number to Discourse topic ID’s / post numbers.
A mapping from bbPress topic slug to Discourse topic ID is included in the importer, so you would need to expand on those. That would imply some code to create extra (Post) permalinks based on the existing topic permalinks.
So for instance if /t/blah maps to topic #123 then
/t/blah/page/2 would map to /t/slug/123/20
/t/blah/page/3 would map to /t/slug/123/40
and so on.