Q: How can I load only desired file types during the browsing?
Q: How to exclude specific file extensions (e.g. TXT) from browsing through directory?
Q: IrfanView can load e.g. CR3 files, but the files are not shown in the Thumbnail window?
A: Go to "Properties->Extensions", edit the file extensions in field "Load custom file types"; delete unwanted or add special (but supported!) extensions at the end (use '|' as delimiter). Press OK and later F5 in IrfanView to reload the folder.