Problems since update to WP 5.6

Hello, As an absolute beginner, I use the Fotografie Pro Theme 3.3. Since I installed the update to WP 5.6, there are numerous problems: 1.) Catch Gallery: - The plugin starts but has no function anymore, a gallery is created without using the plugin (no gallery settings anymore). - I can click on existing catch galleries, then the page turns completely white and I only see the pencil and the cross. If I click on the pencil, I can still edit the gallery (created under 5.5) and also see the catch gallery settings on the right side of the page. 2.) Normal Gallery (without Catch as this does not work) - With a new gallery (created under 5.6) no Catch Gallery is created anymore, I cannot change any properties in the normal WP Gallery. The image size of the gallery remains "large" even if I click on preview or small... Are these errors known? How can I solve them? Thanks in advance Andreas