Data import can be a huge pain, but I find it works a lot better if you use the old data import wizard.
First take the file you want to import and convert it to CSV by selecting the file type when saving it in excel:

Then, from Power Apps, select the gear in the top right corner and select Power Platform Admin Center. In the admin center, select your environment and hit Settings. From there you can get into the data import wizard:

Select IMPORT DATA and choose your CSV file, then follow the wizard. This works out much better and doesn't have any of the errors you see when trying to import using the new Power Platform model.