Claris just released FileMaker 19.2 and MBS FileMaker Plugin works fine with it. We have been testing the new version for weeks and not yet found an issue.
Please make sure you use version 10.5 or better 10.6pr2 with latest Big Sur fixes.
FileMaker Pro 19.2.1 Updater Release Notes
Claris FileMaker Server 19.2.1 Release Notes
Claris FileMaker Cloud 220.127.116.11 Release Notes
But there is a new feature in FileMaker to allow developers to disallow plugins to run scripts or do SQL queries. This is done with a new extended privilege named fmplugin. Or in a per plugin specific version you can add one named fmpluginXXXX, where XXXX is the 4 letter code of the plugin, e.g. MBSP for our MBS Plugin.
If a plugin tries to run a script or execute a SQL statement in a target file, FileMaker scans for fmplugin privilege sets. If the current account in the target file does have the privilege granted for either all plugins or specifically MBS Plugin, the operation is allowed. Otherwise you may see error codes and your scripts may not get the desired action.
FileMaker Pro adds the new privilege automatically to a new file for you. As old files don't have the privilege (unless you add it), plugins should work as before. But for the new files, this can cause plugin functions which involve starting scripts or running SQL commands to not work as permissions get denied to do so. Error code 825 as far as we see. This may affect our capabilities to search relationship graph, show field or table names. Also Audit functions may be affected and our FMSQL functions of course. This is not always directly visible as for example FM.QueryTableNames, XML.Import or JSON.Import use SQL internally.
There is an exception, that if you have admin privileges, you can allow access via an UI code, which can create a permanent link between files and allow access without privilege set.
Let us know if you find an issue or have a question.