Hi Admin
Firstly great work on the improvements in the builder
Found a glitch , workaround and solution for you

Create a search filter...
the default is searchinstance1... searchinstance2...
but if you provide a search instance name rather than use the default such as "my item search"
When you search or save a new record you will get unencapsulated T String error

Reason
The search instance name contains spaces

Workaround
Check your search instance name remove spaces in the name
if you experience issues with the filter not working correctly after renaming the search instance name
you may need to delete the filter brick and recreate the filters

Solution
Builder needs to cleanse the search instance name - remove or replace white space in the provided name

@Admin Project created for you name is TSTRINGSearch

BTB300

Fixed now.

Good catch.