Upgrade to Musescore 3. - problems in showing Style

Updated to MS3 in Windows 7 and started working on a nearly finished peace. Style catalogue is visible only poorly. Did not try other features as this is critical for me. Can this version be used in Windows 7? Or is the problem elsewhere? I cannot use the version as it is now on my computer.....

Problems escalate.... Now the peace is unusable in MS2 as it has been saved once by MS3. Any possibility to rescue it? ... Otherwise love this program! Thanks for any tips!