Too many math alphabets used in version normal error

It’s all the DeclareSymbolFont commands, on top of packages such as ammsymb. You only have 16 symbol alphabets in legacy TeX.

One option is to switch to unicode-math, which removes this limit completely.

You can also remove those redefinitions of symbol alphabets. You don’t appear to actually need them.

Usually, if you’re using PDFTeX, you want to pick one math-font package, a matching text-font package, and then load any other alphabets you need with mathalpha or isomath. It is very rare that you would ever want to reload cmex and so forth. Are you copying-and-pasting from some other template that loaded one or two symbols from Computer Modern?

For example, if you load a Times-like main font, you probably want to load newtxmath with newtxtext or tgpagella in PDFTeX, or set your math font to TeX Gyre Termes Math and your main font to a clone of Times in LuaTeX.

You have defined several times the same symbol font; each DeclareSymbolFont declaration uses up a math family.

I reorganized your preamble in sections, so it's easier to spot duplications.

I also added notes about packages not to use. Finally, defining R as mbox{$mathbb{R}$} is wrong: you'll get normal size also in subscripts, for instance. If the aim is to being able to use R and similar in text, don't: there's no gain in writing the set R{} is interesting instead of the set $R$ is interesting (and editors will color your syntax appropriately). I commented out alternative definitions to enable ensuremath, but, I repeat, don't.

documentclass[11pt,letterpaper,twoside]{report}
usepackage[utf8]{inputenc}
usepackage[T1]{fontenc}
usepackage[spanish]{babel}
usepackage[left=2.50cm, right=2.54cm, top=2.54cm, bottom=2.54cm]{geometry}

usepackage{amsmath}
usepackage{amsthm}
%usepackage{txfonts} % bad spacings
usepackage{newtxtext,newtxmath} % fixes the wrong bits in txfonts
%usepackage{amsfonts} % amssymb does it
%usepackage{amssymb} % not along with newtxmath

usepackage{graphicx}
usepackage{biblatex}
%usepackage{enumerate} % not along with enumitem
usepackage[shortlabels]{enumitem}
usepackage[nottoc,notlot,notlof]{tocbibind}
%usepackage{physics} % are you sure?
usepackage{float} 
usepackage{tkz-fct}
usepackage{tkz-euclide}
usepackage{tikz-cd}
usepackage{fancyhdr}

usepackage{cleveref}


%% page styles
pagestyle{fancy}

fancyhf{} 
fancyhead[LO]{nouppercaseleftmark} % En las páginas impares, parte izquierda del encabezado, aparecerá el nombre de capítulo
fancyhead[RE]{nouppercaserightmark} % En las páginas pares, parte derecha del encabezado, aparecerá el nombre de sección
fancyhead[RO,LE]{thepage} % Números de página en las esquinas de los encabezados

% different choices for math
DeclareSymbolFont{cmsymbols}{OMS}{cmsy}{m}{n}
SetSymbolFont{cmsymbols}{bold}{OMS}{cmsy}{b}{n}
DeclareSymbolFont{cmlargesymbols}{OMX}{cmex}{m}{n}
SetSymbolFont{cmlargesymbols}{bold}{OMX}{cmex}{b}{n}

DeclareMathAlphabet{mathbb}{U}{msb}{m}{n}
DeclareSymbolFontAlphabet{mathcal}{cmsymbols}

DeclareMathSymbol{forall}{mathord}{cmsymbols}{"38}
DeclareMathSymbol{exists}{mathord}{cmsymbols}{"39}
DeclareMathSymbol{pi}{mathord}{letters}{"19}
DeclareSymbolFont{cmlargesymbols}{OMX}{cmex}{m}{n}
DeclareMathDelimiter{rbrace} {mathclose}{cmsymbols}{"67}{cmlargesymbols}{"09}
DeclareMathDelimiter{lbrace} {mathopen}{cmsymbols}{"66}{cmlargesymbols}{"08}

% personal commands
DeclareMathOperator{fr}{fr}
DeclareMathOperator{interior}{int}
DeclareMathOperator{diam}{diam}
newcommand*closure[1]{overline{#1}}
newcommand{numberset}[1]{mathbb{#1}}
%newcommand{numberset}[1]{ensuremath{mathbb{#1}}}% not recommended
newcommand{R}{numberset{R}}
newcommand{C}{numberset{C}}
newcommand{F}{numberset{F}}
newcommand{N}{numberset{N}}
newcommand{Z}{numberset{Z}}
newcommand{Q}{numberset{Q}}
newcommand{ap}{phiup}
%newcommand{ap}{ensuremath{phiup}}
newcommand{bd}{bar{d}} 
%newcommand{bd}{ensuremath{bar{d}}}

% various settings
%setlength{parindent}{0mm} % why?

The highest family number used is 9. You should be OK.