Thank you Anke for those examples, Their basic text read operations are similar to mine so that suggests I should be able to read at least 2.5 Mbyte. In the past the largest file I have read was 3.9 MByte but I can no longer read text files that big. I'm testing various file sizes to find the limit or issue.
While searching for information I found two contradictory statements one which suggests the text file is limited by the size of the device (computer?) system memory.Variable Size Limits
The other suggests a limit of about 2 MByte
https://puravidaapps.com/read.php