Colosseum Tool crashes when attempting to extract an iso on both high sierra and mojave. This occurs with 1.0.1. Cannot extract and import textures either, which you say requires a gtx or an atx file, but nothing of the sorts outputs nor can I find anything online about those two file types.
EDIT: Here's the log of the issue: https://drive.google.com/open?id=1tXYc-31jFrslRaJT_zE_tEVwmMjB-zsH
EDIT 2: Hmm... after looking over this issue, seems there is a problem that keeps popping up now and then from past releases. Versions 8.1 and 9.0 did not have this issue, but versions before that was looking for pocket_menu.fsys and other fsys files that did not exist in my rom. As far as I know, these never existed in colosseum, only gale of darkness...
EDIT 3: Found the pocket_menu.fsys on my iso. Not sure why it's not returning positively found. https://drive.google.com/open?id=1NMM1BBxc2v_P4A-Q-X71fV65cWnQwWqc
EDIT 4: After double checking the error, the error points to the Colosseum tool's own source of files, namely, the FSYS Folder. Indeed, the pocket_menu.fsys file was not created upon first opening of Colosseum tool. Maybe that's the problem? Double check the creation of ALL the required files. A screenshot of what I have in that folder. https://drive.google.com/open?id=1nm-CYI8T-Eq24SozP5YH2nCAVT459vxz
EDIT 5: Pocket_menu.fsys is located in MENUFSYS, not FSYS. This was probably a typo, but moving the file from MENUFSYS to FSYS temporarily fixed the problem. Also, another problem cropped up: Pcbox_pocket_menu. It searches for Pcbox_pocket_menu file without a file extension in the correct location. However, since there is a file extension with that particular file, it returns nothing and crashes. MIDEDIT: Same thing with the pcbox_name_entry_menu, pcbox_menu, pda_menu, world_map, and pocketchange_menu. Changing those will fix the issue, and the iso extraction completes.
EDIT 6: after all this. textures still fail to export