First, fasttracking is almost incompatible with use of mangle rules. Once you make it work with the action=fasttrack-connection rule disabled, you can read this and possibly do some modifications.
Second, I wonder from where the belief that dst-address-type=local matches on addresses in connected subnets keeps popping up - what was the original source you’ve used to set it up? I’ve seen this mistake in tens of topics. In reality, address-type=local only matches on any own address of the router. So to avoid assigning a routing-mark to internet → LAN packets in mangle in prerouting, you have to replace dst-address-type=!local by dst-address=!192.168.88.0/24 (or, in more complex cases, you have to create an address-list containing all local subnets). Or instead you can use /routing/rule items to revert the assignment of the routing mark for internet → LAN packets.
Try these two changes and report back - if it is not enough, post the updated configuration.