How do I seal gaps on interior raw brick walls?

-- Caulking the join between the composition wall/cupboards and the brick -- or cover the brick wall(s) with Sheetrock -- some may be sound-deadening material -- but I don't know you can obtain down under! https://www.thespruce.com/does-soundproof-drywall-really-work-1821484 Good luck!! The 'neighbors' may want to join you in working on the noise issues -- if you can hear them they can hear you!

G’day from own under 🙃. Thank you so much for your answer. This is a great idea 💡. I will check it out. Have a great day.

Here in Canada, we have some plastic trims available to clean up the edges that contact the brick wall. The term for the one I am thinking of is called "tear away." It glues on with the manufacturers adhesive/spray. Adhesive is applied to both surfaces and then stapled on to the drywall. It is then mudded over to conceal the trim. When finished, part of the trim is torn away. This part of the trim prevented the mud from going on the brick. always a good idea to tape up the brick until you're finished anyhow. Apply primer and paint and you're done. Hope you can find this trim in your country.

Thanks so much for the advice. I will visit my hardware store and find out. blessings from Australia to Canada : ) Have a great day!

It appears there is a solid tile below the brick, is that correct? You could clean the brick with a good cleaner and brush, allow it to dry, then use the same brick as is on the bottom Extending it up over the brick wall.