I found two sources that consider this license free (at least DFSG)
still remains incompatible with GPL so USE=bindist is required
By section 6.4, it is based on MPL-1.1 (which is in @FSF-APPROVED):
6.4 Origin of the InterBase Public License.
The InterBase Public License V 1.0 is based on the Mozilla Public License V 1.1 with the following changes:
1. The license is published by Inprise Corporation. Only Inprise Corporation can modify the terms applicable to Covered Code.
2. The license can be modified and used for code which is not already governed by this license. Modified versions of the license must be renamed to avoid confusion with Netscape's or Inprise Corporation's public license and must include a description of changes from the InterBase Public License.
3. The name of the license in Exhibit A is the "InterBase Public License".
4. The reference to an alternative license in Exhibit A has been removed.
5. Amendments I, II, III, V, and VI have been deleted.
6. Exhibit A, Netscape Public License has been deleted
7. A new amendment (II) has been added, describing the required and restricted rights to use the trademarks of Inprise Corporation.
Plus, the license is virtually identical to IDPL (which is in @MISC-FREE), except for the added amendments, and some typo fixes.
The bug has been closed via the following commit(s):
Author: Ulrich Müller <email@example.com>
AuthorDate: 2019-08-30 09:31:48 +0000
Commit: Ulrich Müller <firstname.lastname@example.org>
CommitDate: 2019-08-30 09:31:48 +0000
profiles: Add Interbase-1.0 to MISC-FREE license group.
Signed-off-by: Ulrich Müller <email@example.com>
profiles/license_groups | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)