The MSSQL database no longer seems to write to every folder in certain versions.
Please note: You are using MSSQL Server 2019 Express Edition. This version is not officially supported by us!

Try if you can write to the following folder:
C:\Program Files\Microsoft SQL Server\MSSQL15.AMOFFICE\MSSQL\Backup

To get rid of MSSQL Server issues once and for all, we recommend switching from MSSQL Server to PostgreSQL.
We will only support this database server in the future. PostgreSQL is very performant, free and not limited to a maximum size of 10GB.

The switch is very easy:

1. Start the ASA-AMOffice© server management program on your server
2. Switch to the Database tab
3. From there, call the "Database Migration" function

Please note: The conversion of the database can take several hours.
If possible, let the conversion run over the weekend.