You can try:
install 1.1, then 1.0.6 (but skip the uninstall.
I believe 1.1 with 26.1 will install fpc in a folder 2.6.1, so this will be kept.
Otherwise: Copy the fpc folder, after install of 1.1. FInd the file fpc.cfg and fix all pathes inside using a texteditor.
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In both cases you then need to open the options in Lazarus and point to the right fpc