Tinkered with master-slave before but didn't run any site that I thought would justify the time spent. Having said that, did a little digging (revisiting) and discovered (am not a certified DB admin):
Master-master setups might be old technology now. There is now 'Group Replication' which might address the issue you've raised.
Master-master
https://www.digitalocean.com/community/tutorials/how-to-set-up-mysql-master-master-replication
note what it says on that page ... link to new method ...
https://dev.mysql.com/doc/refman/8.0/en/group-replication.html
above is version 8 of MySQL
https://dev.mysql.com/doc/refman/5.7/en/group-replication.html
Think others would be interested in how you get along with this, so please share back your discoveries! ;)
'spirit of sharing', Ken