I think GOG should have a similar feature that steam have. On steam you have the option to create a copy of "uncompressed" screenshot when you take a single one. Here you can only have the option to take it in full quality. To give you a dimension of this 'issue', i have 352 screenshot of cyberpunk 2077. They have between 3~5MB and the folder have a little more than 1GB (1.22GB). For The Witcher 3 (Steam), i have 135 screenshot, the folder have 50MB, they have between 378 KB ~ 1MB.