I am going to make this suggestion from my past experience using another graphic arts program called U-Lead Photo Impact. I believe Corel owned this program for a while, I have Versions 5 and newer Photo Impact Pro 13 that I use exclusively for creating custom designed frames for my artwork. Would like to suggest that since Painter is primarily a digital painting program seems to me that a way of creating custom frames for your finished product within the Painter program would be a very good addition. From my past experience, in the event you need to make some changes to some finished artwork having a .rif file available with all the layers (including layers that you used to create a digital frame) would be a better option than having to recreate the frame all over again using a different program. I believe that such a plug-in or addition to the Painter program would be most helpful having all digital frame information within the native .rif file for editing and/or ability to create other file formats such as jpg, png, tiff, bmp. One of the major problems with creating frames in U-Lead is that the custom framing options for 2D, 3D and Magic Frame are almost impossible to recreate exactly the same unless you jot down on paper the exact details of how you produced your custom frame. The only option that is easy to use over again exactly is the Classic Frame, yet these frames tend to cut off at the perimeters a lot of the borderline space of your digital image. Again the Classic Frames are not custom designed there more like template frames, whereas the 2D, 3D, and Magic Frames allow you to create and more closely coordinate colors of your frame to match your digital image that is being framed.
Secondly, I really like using the KPT Collection as a plug-in in older 32 bit version Painter programs such as 8 and 9.5. I find this plug-in especially useful for creating backgrounds for my personal web-site art gallery I have on line. This plug-in has a lot of good features to create unique backgrounds for my web site art gallery pages. This plug-in does not work in the latest version of Painter that I have 2020 a 64 bit version program. Is there anything newer out there that replaces the older 32 bit version of this plug-in that can be added to Painter 2020? If not I would certainly like to see this plug-in resurrected for use in more current versions of Painter.
It has it's limitations , but Topaz Studio can do a lot of what you mention.
Another option AKVIS ArtSuite akvis.com/.../index.php
Only Another option is to download picture frames from the internet and import them as a layer.