Hello Fuka1,
I noticed the issue is one known issue. As we still need the system solution. You can follow the steps below to remove the dependencies to the solution you are trying to delete.and deploy it as an upgrade. The steps below are the steps you would follow in the example scenario described in the Cause section.
1. In the source environment where System Solution was created, update System Solution to remove the reference to the custom security role:
a. Access the source environment as a user with the System Administrator or System Customizer security role.
b. Navigate to Settings and then click Solutions.
c. Open the other solution mentioned in the error message (system solution).
d. In the Version field, increase the version number.
e. On the left side of the page, locate the component and then remove it. In the example provided, you would click Security Roles, select the custom security role, and then click Remove.
f. Click Save and then click Publish All Customizations.
2. Click Export Solution and choose to export the solution as Managed.
3. In the target environment (the organization where you encountered the error), import the updated solution (System Solution):
a. Access the target environment as a user with the System Administrator or System Customizer security role.
b. Navigate to Settings and then click Solutions.
c. Click Import and browse to the updated solution file you exported.
d. Click Next. You will see a notice that "This solution package contains an update for a solution that is already installed".
e. Click Next and select the Stage for upgrade checkbox.
f. Click Import.
g. After the import completes, click Apply Solution Upgrade. NOTE: If you closed the import dialog without clicking Apply Solution Upgrade, you can select the solution in the Solutions list and then click Apply Solution Upgrade.
4. Now that the dependency has been removed from System Solution, try to delete mentioned solution again.
Reference Doc: https://support.microsoft.com/en-us/help/4346631/cannot-uninstall-solution-error-occurs-in-dynamics-365
Best Regards
Johnny
