The reason for this incompatibility is the permanent development of the Locus application and the Android itself as well. Some functions simply cannot be developed for older Android devices.
The solution is to install the latest Locus Map version that supports your version of Android.
Locus Map Pro
To use an older Locus Map Pro, you have to purchase a license for Locus Map Classic. Please do so in the Google Play Store in an Android emulator on your PC, running Android higher than 5.0 (e.g. Bluestacks) - the license validation will work for the old Locus Map Pro as well.
Locus Map Free 3.37.2 (23,8 MB)
Locus Map Pro 3.37.2 (23,2 MB)
Locus Map Free 3.31.3 (23,8 MB)
Locus Map Pro 3.31.3 (23,2 MB)
Locus Map Free 3.15.3 (18,5 MB)
Locus Map Pro 3.15.3 (18,2 MB)
Locus Map Free 3.5.3(15,4 MB)
Locus Map Pro 3.5.3 (15,3 MB)
Locus Map Free 2.13.1 (9 MB)
Locus Map Pro 2.13.1 (9 MB)