Good day, I have had an issue with my PC and as such am WAY behind with all the topics. Is there any way to just make all topics as read and start from scratch, please?
I am afraid not.
Discourse gives users credit for reading
and posts credit for being read.
although one can mark unread a topic. obviously .
@markadewet
maybe the dismiss new button is an option 
@current_user OK, i will bite, where IS this supposed “dismiss new” button???
@markadewet
for the easiest intuitive handling discourse offers
the dismiss new button topmost right oriented.
you may be forced to visit each of the categories
@current_user Thank you, finally found it, AFTER clicking on the down arrow NEXT to “New Topic”
EDIT: Very strange behaviour, the down arrow does NOT always seem to show, when there are new topics. Oh well, at least it is something.
you’re welcome 
and welcome to the next-generation-credit-forum 