Your ISP seems to be a bit over zealous on forcing an upgrade to php 8. Version 7.4 is still supported for a while yet.
There was a previous thread about this topic
End result is that most RW devs, including RealMac, have not tested their products for php 8 compatibility (due to 7.4 still being supported).
Solution is either to use a HTML contact form (see posts), an obfuscated mailto: link, or in your case change hosts to a company less eager to be up to date at the exclusion of everything else.