Bash has problems with cmdline nft cmd vs script

linux mint. uname -r yields 5.15.0-56. dpkg-query -l bash yields 5.1.6ubuntu1.
My script shows this problematic output when bash -x script invoked:

attrib =' '\''{type nat hook prerouting  priority mangle+10;}'\'' '

But from the commandline:

sudo nft create chain inet firewalld mangle_PREROUTING '{ type nat hook prerouting priority mangle + 10 ;}'

It works fine.
This script replicates the fedora nft tree.

 x=$(sudo nft -a list tables)   
 if [[ $x != '' ]]; then  
     sudo nft flush table inet firewalld  
      sudo nft delete table inet firewalld  
 fi  
 sudo nft create table inet firewalld  
 for stage in mangle net filter;do  
     for step in _PREROUTING _OUTPUT _INPUT _IN_workstation; do
      meat=${step/_/}   
       priority=${stage/_/}   
       a=${step/_[a-zA-Z]+/_}   
       b=${stage/_[a-zA-Z]+/_}   
       if [[ $stage =="__"]]; then   
            type="nat"   
       else
            type="filter"   
       fi.   
       hook=${meat,,}   #translate to all lowercase.  
       attrib=" '{ type "$type" hook "$hook" priority "$priority"+10;}'"   

      
    if[[ $a$b == "__" ]]; then   
        cmd=" insert rule inet firewalld $stage$step" ;   
         sudo nft $cmd  
     else  
         cmd=" create chain inet firewalld $stage$step $attrib";   
        sudo nft $cmd  
    fi  
     done  
  done  

Removing the single quotes around the curly braces was the answer. I tried this because I figured the shell script (and sudo) were doing a fork/exec, for nft, with no shell interpretation.